Ground-Water Quality Classification and Recommended Septic Tank Soil- Absorption-System Density Maps, Cache Valley, Cache County, Utah

GROUND-WATER QUALITY CLASSIFICATION AND RECOMMENDED SEPTIC TANK SOIL- ABSORPTION-SYSTEM DENSITY MAPS, CACHE VALLEY, CACHE COUNTY, UTAH

by Mike Lowe, Janae Wallace, and Charles E. Bishop Utah Geological Survey

Cover Photograph: flowing well in the Cache Valley discharge area. Photo by Janae Wallace.

Although this product represents the work of professional scientists, the Utah Department of Natural Resources, Utah Geological Survey, makes no warranty, expressed or implied, regarding its suitability for any particular use. The Utah Department of Natural Resources, Utah Geological Survey, shall not be liable under any circumstances for any direct, indirect, special, incidental, or consequential damages with respect to claims by users of this product.

ISBN 1-55791-686-1

SPECIAL STUDY 101 Utah Geological Survey a division of 2003 Utah Department of Natural Resources STATE OF UTAH Michael O. Leavitt, Governor

DEPARTMENT OF NATURAL RESOURCES Robert Morgan, Executive Director

UTAH GEOLOGICAL SURVEY Richard G. Allis, Director

UGS Board Member Representing Robert Robison (Chairman) ...... Minerals (Industrial) Geoffrey Bedell...... Minerals (Metals) Stephen Church ...... Minerals (Oil and Gas) E.H. Deedee O’Brien ...... Public-at-Large Craig Nelson ...... Engineering Geology Charles Semborski ...... Minerals (Coal) Ronald Bruhn ...... Scientific Kevin Carter, Trust Lands Administration ...... Ex officio member

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UGS Editorial Staff J. Stringfellow ...... Editor Vicky Clarke, Sharon Hamre...... Graphic Artists James W. Parker, Lori Douglas ...... Cartographers

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TABLE OF CONTENTS

ABSTRACT ...... 1 INTRODUCTION ...... 1 Purpose and Scope ...... 3 Ground-Water Quality Classification ...... 3 Septic-Tank Density/Water-Quality Degradation Analysis ...... 3 Well Numbering System ...... 4 Location and Geography ...... 5 Climate ...... 5 PREVIOUS INVESTIGATIONS ...... 5 GEOLOGIC SETTING ...... 6 GROUND-WATER CONDITIONS ...... 6 Introduction ...... 6 Basin-Fill Aquifer ...... 7 Occurrence ...... 7 Depth to Ground Water ...... 7 Ground-Water Flow ...... 7 Recharge and Discharge ...... 7 Ground-Water Quality ...... 7 GROUND-WATER QUALITY CLASSIFICATION ...... 11 Introduction ...... 11 Results ...... 11 Total-Dissolved-Solids Concentrations ...... 11 Nitrate Concentrations ...... 11 Dissolved-Iron Concentrations ...... 13 Sulfate Concentrations ...... 15 Chloride Concentrations ...... 15 Other Constituents ...... 16 Resulting Ground-Water Quality Classification ...... 17 Class IA - Pristine ground water ...... 17 Class II - Drinking Water Quality ground water ...... 17 Class III - Limited Use ground water ...... 17 Land-Use Planning Considerations ...... 17 Current beneficial uses of ground water ...... 17 Potential for ground-water quality degradation ...... 17 Possible land-use-planning applications of this ground-water quality classification ...... 17 SEPTIC-TANK DENSITY/WATER-QUALITY DEGRADATION ANALYSIS ...... 17 Introduction ...... 17 Ground-Water Contamination from Septic-Tank Systems ...... 18 Pathogens ...... 18 Household and Industrial Chemicals ...... 18 Phosphate ...... 18 Nitrate ...... 18 The Mass-Balance Approach ...... 19 General Methods ...... 19 Limitations ...... 19 Ground-Water Flow Calculations ...... 19 Introduction ...... 19 Computer Modeling ...... 19 Description of model of Kariya and others (1994) ...... 20 Results ...... 21 Modeling Limitations ...... 21 Septic-Tank-System/Water-Quality Degradation Analyses ...... 21 Introduction ...... 21 Results ...... 22 Domain 1 ...... 22 Domain 4 ...... 22 Shallow Unconfined Ground-Water Issues ...... 26 Recommendations for Land-Use Planning ...... 27 SUMMARY AND CONCLUSIONS ...... 27 ACKNOWLEDGMENTS ...... 28 REFERENCES ...... 29 FIGURES

Figure 1. Geographic features, Cache Valley, Cache County, Utah ...... 2 Figure 2. Numbering system for wells in Utah ...... 4 Figure 3. Schematic block diagram showing ground-water conditions in Cache Valley ...... 6 Figure 4. Change of water level in Cache Valley ...... 8 Figure 5. Relative water levels in wells in recharge and discharge areas ...... 9 Figure 6. Recharge areas in Cache Valley ...... 10 Figure 7. Percentage of wells in shallow, medium, deep, and unknown perforation intervals ...... 12 Figure 8. Relationship between well depth and total-dissolved-solids concentrations ...... 12 Figure 9. Percentage of wells in each hydrogeologic setting sampled for TDS concentrations ...... 13 Figure 10. Percentage of wells in shallow, medium, and deep perforation-depth intervals that are less than 3 mg/L, between 3 and 10 mg/L, and greater than 10 mg/L nitrate ...... 14 Figure 11. Well depth versus nitrate concentration ...... 14 Figure 12. Percentage of wells in each hydrogeologic-setting category that are less than 3 mg/L, between 3 and 10 mg/L, and 10 mg/L or greater nitrate ...... 15 Figure 13. Iron concentration versus well depth ...... 16 Figure 14. Chloride concentration versus well depth ...... 16 Figures 15a-l. Projected septic-tank density versus nitrate concentration for domains 1-12 ...... 23, 24 Figure 16. Recommended lot size for ground-water flow domains in Cache Valley ...... 25

TABLES

Table 1. Ground-water quality classes ...... 3 Table 2. 1990 Hydrologic budget for Cache Valley ...... 7 Table 3. Typical characteristics of wastewater from septic-tank systems ...... 18 Table 4. Cities/towns and land area within each ground-water flow domain ...... 21 Table 5. Parameters used to perform a mass-balance analysis for each ground-water flow domain ...... 22 Table 6. Results of mass-balance analysis ...... 26 Table 7. Physical characteristics of the unconfined aquifer in Cache Valley ...... 27

Appendix A.1. EPA primary ground-water quality standards and analytical methods ...... 32 Appendix A.2. Water-quality data ...... 35 Appendix B. Generalized stratigraphy of Cache Valley, Cache County, Utah ...... 39

PLATES

Plate 1. Total-dissolved-solids (TDS) concentration map for the principal basin-fill aquifer Plate 2. Graduated-symbol map of total-dissolved-solids concentration Plate 3. Nitrate concentration map of the principal basin-fill aquifer Plate 4. Graduated-symbol map of nitrate concentration Plate 5. Graduated-symbol map of iron concentration Plate 6. Graduated-symbol map of sulfate concentration Plate 7. Graduated-symbol map of chloride concentration Plate 8. Ground-water quality classification map for the principal basin-fill aquifer Plate 9. Recommended septic-system density based on ground-water flow domain Plate 10. Recommended septic-system density for land-use planning based on ground-water flow domain GROUND-WATER QUALITY CLASSIFICATION AND RECOMMENDED SEPTIC TANK SOIL- ABSORPTION-SYSTEM DENSITY MAPS, CACHE VALLEY, CACHE COUNTY, UTAH

by Mike Lowe, Janae Wallace, and Charles E. Bishop Utah Geological Survey

ABSTRACT The results of our ground-water flow modeling using the mass-balance approach indicate that three categories of rec- Cache Valley in northern Utah is experiencing an in- ommended maximum septic-system densities are appropriate crease in residential development. Most of this development, for development using septic tank soil-absorption systems much of which uses septic tank soil-absorption systems for for wastewater disposal: one-third, one-fifth, and one-tenth wastewater disposal, is on unconsolidated deposits of the systems per acre (0.33, 0.2, and 0.1 systems/acre [0.13, 0.08, basin-fill aquifer, a major source of drinking water. The and 0.04 systems/hm2]); these categories correspond to 3, 5, purposes of our studies are to: (1) classify the ground-water and 10 acres per septic system (1.2, 2, and 4 hm2/system), re- quality of the principal aquifer, based mainly on total-dis- spectively. The recommended maximum septic-system den- solved-solids concentrations, to formally identify and docu- sities are based on hydrogeologic parameters incorporated in ment the beneficial use of the valley’s ground-water re- the ground-water flow model and geographically divided source, and (2) apply a ground-water flow model using a into 12 ground-water flow domains (background nitrate con- mass-balance approach to determine the potential impact of centrations ranging from 0.09 to 6.58 mg/L) on the basis of projected increased numbers of septic-tank systems on water flow-volume similarities. In addition to a map showing the quality in the Cache Valley basin-fill aquifer and thereby rec- model output results, we provide a land-use-planning map ommend appropriate septic-system density requirements to where model output boundaries have been adjusted to cultur- limit water-quality degradation. al and geographic features such as streets and water bodies. The quality of water in the Cache Valley basin-fill aquifer is generally good. Cache Valley ground water is classified as Class IA (Pristine; 84 percent) and Class II (Drink- INTRODUCTION ing Water Quality; 16 percent), based on chemical analyses of water obtained from 163 wells sampled during fall 1997 Cache Valley, Cache County, is a rural area in northern and winter/spring 1998-99. Total-dissolved-solids concentrations in Cache Valley’s principal aquifer range from 178 to Utah (figure 1) experiencing an increase in residential devel- 1,758 mg/L, and average 393 mg/L. Nitrate-plus-nitrite con- opment. Most of this development, much of which uses sep- centrations in Cache Valley’s principal aquifer range from tic tank soil-absorption systems for wastewater disposal, is less than 0.02 to 35.77 mg/L, with an average (background) on unconsolidated deposits of the principal basin-fill aquifer. nitrate concentration of 0.68 mg/L. Ground water, mostly from the basin-fill aquifer, provides Nitrogen in the form of nitrate is one of the principal almost all of the drinking-water supply in Cache Valley. indicators of pollution from septic tank soil-absorption sys- Preservation of ground-water quality and the potential for tems. In the mass-balance approach, the nitrogen mass from ground-water quality degradation are critical issues that the projected additional septic tanks is added to the current should be considered in determining the extent and nature of nitrogen mass and then diluted with the amount of ground- future development in Cache Valley. Local government offi- water flow available for mixing plus the water added by the cials in Cache County have expressed concern about the septic-tank systems themselves. We used a U.S. Geological potential impact that development may have on ground- Survey ground-water flow model to estimate, for different water quality, particularly development that uses septic tank areas of Cache Valley, ground-water flow available for mix- soil-absorption systems for wastewater disposal. Local gov- ing in the principal basin-fill aquifer, the major control on ernment officials would like to formally identify current projected aquifer nitrate concentration in the mass-balance ground-water quality to provide a basis for defendable land- approach. While there are many caveats to applying this use regulations to protect ground-water quality; they would mass-balance approach, we think it is a useful and cost-effec- also like a scientific basis for determining recommended tive approach to use in land-use planning. densities for septic-tank systems as a land-use planning tool. 2 Utah Geological Survey

Figure 1. Geographic features, Cache Valley, Cache County, Utah. Special Study 101 3

Purpose and Scope aquifer, but the results from these sources were not used in the ground-water quality classification because the shallow The purposes of our studies are to: (1) classify the unconfined aquifer is generally not used for drinking water. ground-water quality of the principal (drinking water) The wells and spring were sampled by the Utah Division of aquifers to formally identify and document the beneficial use Water Quality during fall 1997 and winter/spring 1998; the of Cache Valley’s ground-water resource, and (2) apply a water samples were analyzed for general chemistry and ground-water flow model using a mass-balance approach to nutrient content by the Utah Division of Epidemiology and determine the potential impact of projected increased num- Laboratory Services. Water from 15 of the wells was not bers of septic-tank systems on water quality in the basin-fill analyzed for iron, water from six wells was not analyzed for aquifer and thereby recommend appropriate septic-system- sulfate, and water from another six wells was not analyzed density requirements. Together, these two study components for chloride. Water from 46 of the wells was analyzed for will provide land-use planners with a tool to use in approv- organics and pesticides, and water from 13 was analyzed for ing new development in a manner that will be protective of radionuclides. Wells yielding ground water that exceeded ground-water quality. water-quality (health) standards in place at the time of sampling were resampled, sometimes multiple times, to verify Ground-Water Quality Classification results. A summary of the constituents analyzed for, ground- water quality (health) standards for some constituents, and Ground-water quality classes under the Utah Water selected water-quality data are presented in appendix A. Quality Board classification scheme are based largely on total-dissolved-solids (TDS) concentrations (table 1) (for the ranges of chemical-constituent concentrations used in this Septic-Tank Density/Water-Quality Degradation report, including those for TDS, mg/L equals parts per mil- Analysis lion). If any contaminant exceeds Utah’s ground-water quality (health) standards (and, if human caused, cannot be To provide recommended septic-tank densities for Cache cleaned up within a reasonable time period), the ground Valley using the mass-balance approach to evaluate potential water is classified as Class III, Limited Use ground water. water-quality degradation, we first used the digital ground- In order to classify the quality of ground water in the water flow model of Kariya and others (1994) to estimate Cache Valley basin-fill aquifer, we selected 163 wells for ground-water flow available for mixing (dilution) in each of sampling from three depth categories: (1) 37 of the wells are the model’s cells (representing a specific land-surface area shallow wells (less than 100 feet [30 m] deep) completed in ranging from 0.2 to 1 square mile [0.5-2.6 km2]) for the the principal aquifer, (2) 79 of the wells are of medium depth model’s uppermost layer. We then (1) grouped cells into 11 (100-200 feet [30-60 m]) completed in the principal aquifer, ground-water flow domains (geographic areas having similar and (3) 42 of the wells are deep wells (greater than 200 feet characteristics of flow-volume per unit area), and defined a [60 m] deep) completed in the principal aquifer. Depth is not 12th domain in the Clarkston area; (2) determined areas, known for five of the sampled wells presumed to be com- ground-water flow volumes, estimated number of existing pleted in the principal aquifer. We also sampled one well and septic-tank systems, and ambient (background) nitrate con- a spring producing water from the shallow unconfined centrations for each domain; and (3) calculated projected

Table 1. Ground-water quality classes under the Utah Water Quality Board’s total-dissolved-solids- (TDS) based classification system (modified from Utah Division of Water Quality, 1998).

Ground-Water Quality Class TDS Concentration Beneficial Use

Class IA/IB1/IC2 less than 500 mg/L3 Pristine/Irreplaceable/EcologicallyImportant

Class II 500 to less than 3,000 mg/L Drinking Water4

Class III 3,000 to less than 10,000 mg/L Limited Use5

Class IV 10,000 mg/L and greater Saline6

1Irreplaceable ground water (Class IB) is a source of water for a community public drinking-water system for which no other reliable supply of comparable quality and quantity is available due to economic or institutional constraints; it is a ground-water quality class that is not based on TDS. 2Ecologically Important ground water (Class IC) is a source of ground-water discharge important to the continued existence of wildlife habi- tat; it is a ground-water quality class that is not based on TDS. 3For concentrations less than 7,000 mg/L, mg/L is about equal to parts per million (ppm). 4Water having TDS concentrations in the upper range of this class must generally undergo some treatment before being used as drinking water. 5Generally used for industrial purposes. 6May have economic value as brine. 4 Utah Geological Survey nitrogen loadings in each domain based on increasing num- Well Numbering System bers of septic-tank soil-absorption systems, using the appropriate amount of wastewater and accompanying nitrogen The numbering system for wells in this study is based on load introduced per septic-tank system. Using an allowable the Federal Government cadastral land-survey system that degradation of ground water, with respect to nitrate, of 1 divides Utah into four quadrants (A-D) separated by the Salt mg/L (the amount of water-quality degradation determined to Lake Base Line and Meridian (figure 2). The study area be acceptable by local government officials), we were then includes parts of both the northeastern and northwestern able to derive septic-tank density recommendations for each quadrants (A and B). The wells are numbered with this quad- domain. At the request of the Cache County Planning De- rant letter (A or B), followed by township and range, all partment, a second septic-tank density map was produced enclosed in parentheses. The next set of characters indicates with domain boundaries adjusted slightly to match geo- the section, quarter section, quarter-quarter section, and quar- graphic and cultural features to facilitate land-use planning ter-quarter-quarter section designated by letters a through d, purposes. indicating the northeastern, northwestern, southwestern, and

Figure 2. Numbering system for wells in Utah (see text for additional explanation). Special Study 101 5 southeastern quadrants, respectively. A number after the PREVIOUS INVESTIGATIONS hyphen corresponds to an individual well within a quarter- quarter-quarter section. For example, the well (A-14-1) Detailed geologic investigations in the Cache Valley area 9adb-1 would be the first well in the northwestern quarter of began with Bailey’s (1927) studies of the geology of the Bear the southeastern quarter of the northeastern quarter of section River Range and the Bear River Range (East Cache) fault. 9, Township 14 North, Range 1 East (NW1/4SE1/4NE1/4 sec- Williams (1948) studied Paleozoic rocks in the area, and tion 9, T. 14 N., R. 1. E.). included a measured section of the Swan Peak Formation in Green Canyon. Ross (1951) included a description of the Location and Geography Garden City and Swan Peak Formations in Green Canyon. Haynie (1957) examined the Worm Creek Quartzite Member Cache Valley (figure 1) is a north-south-trending valley of the St. Charles Formation in Green Canyon. Williams with an area of about 660 square miles (1,710 km2) in north- (1958) reported on further studies of stratigraphy and geo- eastern Utah and southeastern Idaho. About 365 square logic history in Cache County. Galloway (1970) studied the miles (945 km2) of the valley is in Utah. Cache Valley is in structural geology of the eastern portion of the Smithfield the Cache Valley section of the Middle Rocky Mountains quadrangle. Van Dorston (1970) studied the Swan Peak For- physiographic province (Stokes, 1977). In Utah, Cache Val- mation in the Bear River Range. Gardiner (1974) studied the ley is bordered by the Bear River Range to the east, the Nounan Formation in the Bear River Range and Wellsville Wellsville Mountains to the southwest, and Clarkston Moun- Mountains. Mendenhall (1975) studied the structural geolo- tain to the northwest. The valley floor ranges in elevation gy and mapped the Richmond quadrangle in northeastern from about 4,400 to 5,400 feet (1,340-1,650 m). Peaks in the Cache Valley. Oaks and others (1977) summarized Middle Wellsville Mountains and Bear River Range reach elevations Ordovician stratigraphy in northern Utah and southern and above 9,000 feet (2,700 m). central Idaho, including the Bear River Range. Taylor and The Bear River, the largest tributary to Great Salt Lake, Palmer (1981) and Taylor and others (1981) studied Cambri- flows through Cache Valley, entering Utah from the north an and Ordovician stratigraphy and paleontology in the Bear River Range and measured a section in Green Canyon. Mor- and exiting Cache Valley between Clarkston Mountain and gan (1988) studied the petrology of the Garden City Forma- the Wellsville Mountains. Several large tributaries to the tion in the Bear River Range. Oaks and Runnells (1992) Bear River, including the Logan River, Blacksmith Fork, and studied the Wasatch Formation in the Bear River Range. Little Bear River, originate in the mountains surrounding Williams (1962) studied Bonneville lake-cycle deposits in Cache Valley in Utah. Cache Valley. Available population and land-use statistics are for Cache Many investigators have studied the Salt Lake Forma- County as a whole; most people in the county live in Cache tion in Cache Valley (Williams, 1948, 1964; Smith, 1953; Valley. From 1990-2001, population in Cache County in- Adamson 1955; and Adamson and others, 1955). Galloway creased by 2.5 percent (Demographic and Economic Analy- (1970) redesignated the Salt Lake Group as the Salt Lake sis Section, 2002). The July 1, 2001, population of Cache Formation. Modern studies of the Salt Lake Formation in- County is estimated at 93,372; projected population is clude those of Smith (1997), Goessel (1999), Goessel and 143,040 by 2030 (Demographic and Economic Analysis Sec- others (1999), Oaks and others (1999), and Oaks (2000). tion, 2000). Mullens and Izett (1963), Mendenhall (1975), Oviatt (1986a,b), Brummer and McCalpin (1990), Evans and others Climate (1991), Lowe and Galloway (1993), Barker and Barker (1993), and Biek and others (2001) produced 7.5-minute As is typical of the “back valleys” east of the Wasatch geologic quadrangle maps of the Cache Valley area. Dover Range, Cache Valley is characterized by large daily and sea- (1985) mapped geology of the Logan 30' x 60' quadrangle. sonal temperature ranges (Utah Division of Water Resources, Lowe (1987) mapped the surficial geology of the Smithfield 1992). Normal climatic information (1961-90 period) is 7.5-minute quadrangle. available from four weather stations in Cache Valley (Logan Peterson (1946) conducted an early investigation of the Radio KVNU, Logan Utah State University, Richmond, and quantity of ground-water supply available in Cache Valley. Trenton/Lewiston), and average climatic information is Beer (1967) evaluated southern Cache Valley’s basin-fill available from the Logan Utah State Experiment Station and aquifer to determine those areas having the best potential for the College Ward Utah State University Experiment Farm water development based on available water supply, chemi- (Ashcroft and others, 1992); the information reported below cal quality, and potential ground-water withdrawal rates. A is taken from Ashcroft and others (1992). Because the nor- detailed Cache Valley ground-water study was made by mal climatic information represents a more complete data Bjorklund and McGreevy (1971). Anderson and others set, those values are discussed herein. Temperatures reach a (1994) mapped ground-water recharge and discharge areas normal maximum of 90.0°F (32.2°C) (Richmond station) for Cache Valley’s basin-fill aquifer. Kariya and others and a normal minimum of 10.2ºF (-12.1°C) (Trenton/Lewis- (1994) produced a ground-water flow model for the basin-fill ton station); the normal mean temperature ranges from 44.8 aquifer. Lowe and Wallace (1999a,b, 2001; Wallace and to 48.5°F (7.1-9.2°C). Normal mean precipitation ranges Lowe, 1999) delineated ground-water quality of the basin-fill from 16.6 to 19.5 inches (42.1-49.5 cm); normal mean evap- aquifer. Robinson (1999) characterized the chemistry and otranspiration ranges from 40.9 to 45.3 inches (103.9-115.0 hydrostratigraphy of ground-water and surface-water inter- cm). The average number of frost-free days ranges from 112 action in the Cache Valley basin-fill aquifer. Erickson and at Trenton/Lewiston to 158 at Logan Utah State University. Mortensen (1974) mapped soils in the Cache Valley area. 6 Utah Geological Survey

GEOLOGIC SETTING ness is near the eastern margin of the valley just south of Logan (Evans and Oaks, 1996). The basin fill consists most- Structurally, Cache Valley is bounded by north-striking, ly of fluvial and lacustrine deposits that interfinger with allu- high-angle normal faults (the East Cache and West Cache vial-fan and, to a lesser extent, deltaic and landslide deposits fault zones) and forms the southern end of a series of half- along the valley margins (Lowe, 1987; Lowe and Galloway, grabens within an extensional corridor between the Wasatch 1993; Evans and Oaks, 1996). Much of the Cache Valley and Teton normal fault systems (Evans and Oaks, 1996). floor is covered with offshore lacustrine silt and clay deposit- Both the East Cache and West Cache fault zones have been ed during the Bonneville lake cycle between about 12 and 26 subdivided into three segments and show evidence of recur- ka (Oviatt and others, 1992, figure 3). At least one other rent Quaternary movement, including Holocene events thick (up to 80 feet [24 m]), correlatable unit of offshore (McCalpin, 1994; Black and others, 1999). lacustrine silt and clay is present within the basin-fill The mountains surrounding Cache Valley consist prima- deposits in Cache Valley; Lowe (1987) tentatively interprets rily of Precambrian to Permian sedimentary and metamor- these fine-grained sediments as having been deposited during phic rocks, predominantly limestone, dolomite, shale, and the Little Valley lake cycle sometime between 90,000 and quartzite (Williams, 1958; Bjorklund and McGreevy, 1971). 150,000 years ago (Scott and others, 1983). The Tertiary Salt Lake Formation, primarily conglomerate and tuffaceous sandstone, is exposed in an almost continuous belt in the foothills surrounding the valley and underlies GROUND-WATER CONDITIONS Quaternary deposits within Cache Valley (Williams, 1962; Evans and Oaks, 1996). The characteristics of stratigraphic Introduction units in the Cache Valley drainage basin are summarized in appendix B. Ground water in the Cache Valley area occurs in two The valley floor in Cache Valley is underlain by uncon- types of aquifers: (1) fractured bedrock and Tertiary semi- solidated basin fill of varying thickness. The greatest thick- consolidated rocks, and (2) unconsolidated deposits. The

Figure 3. Schematic block diagram showing ground-water conditions in Cache Valley, Cache County, Utah (modified from Kariya and others, 1994). Special Study 101 7 hydrostratigraphy of rock units in the Cache Valley drainage Ground-Water Flow basin is summarized in appendix B. Ground water in fractured-rock aquifers is recharged primarily from infiltration of Ground-water flow in Cache Valley’s principal aquifer is precipitation and stream flow, and flows primarily through north-northwest in southern Cache Valley; in most of the val- fractures and, in carbonate units, through solution channels ley, ground-water flow is typically from adjacent topograph- (Kariya and others, 1994). Although some wells and springs ic highlands toward the valley center, generally toward the in fractured rock are used for public water supply in Cache Bear River (Bjorklund and McGreevy, 1971, plate 4). Hori- Valley, some of the public water supply and most domestic zontal hydraulic gradients range from up to about 400 feet water supply is obtained from wells completed in unconsoli- per mile (76 m/km) near the valley margins on the east side dated deposits of the basin-fill aquifer (Bjorklund and of the valley (Kariya and others, 1994) to less than 4 feet per mile (1 m/km) near the western margin of Logan (Beer, McGreevy, 1971). 1967).

Basin-Fill Aquifer Recharge and Discharge Occurrence Recharge to the basin-fill aquifer system is from infiltration of precipitation, streams, canals, ditches, and irrigated Ground water in Cache Valley occurs under perched, fields, and by subsurface inflow from consolidated rock confined, and unconfined conditions (Bjorklund and along valley margins (Kariya and others, 1994) (table 2). McGreevy, 1971). The basin fill is more than several hun- Most recharge takes place in primary recharge areas (figures dred feet thick at many locations in the valley center (Kariya 5 and 6) along the valley margins where unconsolidated and others, 1994). In the area between Smithfield and New- materials have the greatest permeability and vulnerability to ton, unconsolidated sediments are up to about 1,340 feet (410 surface sources of pollution (Bjorklund and McGreevy, m) thick (Bjorklund and McGreevy, 1971). Because the 1971). Discharge from the basin-fill aquifer includes evapo- basin fill is unconsolidated sediment consisting of multiple, transpiration, well-water withdrawal, and seepage to springs discontinuous layers of silt, sand, and gravel (deposited in and Cutler Reservoir (Kariya and others, 1994) (table 2). Of fluvial, alluvial-fan, landslide, and nearshore lacustrine envi- the major streams in Cache Valley, the Bear River, including ronments) separated by layers of silt and clay (primarily Cutler Reservoir, receives the largest amount of ground- deposited in offshore lacustrine environments) (Bjorklund water discharge as seepage to streams (Kariya and others, and McGreevy, 1971; Lowe, 1987, plate 2; Lowe and Gal- 1994). loway, 1993, plate 2), the principal aquifer consists of a com- plex multiple-aquifer system under both unconfined and confined conditions (Bjorklund and McGreevy, 1971; Kariya Table 2. 1990 hydrologic budget for Cache Valley, Cache and others, 1994) (figure 3). Ground water in the principal County, Utah (from Kariya and others, 1994). aquifer is mostly under unconfined conditions along the margins of Cache Valley (Bjorklund and McGreevy, 1971), but Recharge type Amount (cubic feet per second) is under leaky confined conditions in many areas of the cen- Infiltration 57 ter of the valley where many flowing wells exist (Kariya and Canal seepage 140 others, 1994). Kariya and others (1994) attributed the leaky Stream seepage 3 confined conditions to the discontinuous nature of clay and Other* 96 silt confining layers (figure 3). The boundary between un- TOTAL 296 confined and confined conditions is gradational near the mar- Discharge type Amount (cubic feet per second) gins of the basin. The confined portion of the principal Springs 138 aquifer is typically overlain by a shallow unconfined aquifer Evapotranspiration 87 (Bjorklund and McGreevy, 1971) (figure 3). Water wells 52 Seepage to streams 180 Depth to Ground Water TOTAL 457 Depth to ground water in unconsolidated deposits in *Includes subsurface inflow from adjacent consolidated rock Cache Valley ranges from at or near the ground surface in the and seepage from ephemeral streams. central portion of the valley to more than 300 feet (90 m) along the valley margins (Bjorklund and McGreevy, 1971). Long-term water levels in Cache Valley’s principal aquifer Ground-Water Quality were relatively constant between 1945 and 1982 (Kariya and others, 1994), but declined as much as 13 feet (4 m) from Ground-water quality in Cache Valley’s principal aquifer March 1970 to March 2000 (Burden and others, 2000) (fig- is generally very good. Calcium, magnesium, and bicarbon- ure 4). Seasonal water-level changes range from a few feet ate are the major dissolved constituents. Bjorklund and (less than 1 m) to about 20 feet (6 m) (Kariya and others, McGreevy (1971) found TDS concentrations to be mostly 1994, figure 12). Water levels are generally highest in the below 800 mg/L. However, warm saline ground water hav- summer in northern Cache Valley, Utah, lowest in the sum- ing TDS concentrations in excess of 1,600 mg/L has been mer in southeastern Cache Valley, and show no consistent documented near Newton and may be associated with fault seasonal pattern of water-level fluctuations in southwestern zones (Bjorklund and McGreevy, 1971). Some ground water Cache Valley (Kariya and others, 1994). in the basin-fill aquifer also locally exceeds secondary (non- 8 Utah Geological Survey

112°00′ 111°52′30″ 42°00′

41°45′

Figure 4. Change of water level in Cache Valley, Cache County, Utah, from March 1970 to March 2000 (modified from Burden and other, 2000). Special Study 101 9

Figure 5. Relative water levels in wells in recharge and discharge areas (after Snyder and Lowe, 1998). 10 Utah Geological Survey o o 112 00' 111 45' o R. 2 W. R.1 E. T. 3 E. 111 30' 42 o 00' Lewiston 3

41o 57' 30" Cove Clarkston

T.14 N. Bear T.14 N.

Richmond Trenton R Newton iver k ee Cr

mmi t Su Amalga

Cutl Smithfield er

s e Hyde Park r v

i r BEAR

er Riv n o ga 41 45' Logan Lo RIVER 41 o 45'

Mendon Providence RANGE L it tle

T.11 N. Nibley T.11 N.

Wellsville B Hyrum ea Fork

r Blacksmith

e r Paradise o 112 00'

Avon

T. 9 N. T. 9 N.

41 o 30' 41 o 30'

Explanation o T. 3 E.

Recharge Area 111 30'

Primary recharge area, bedrock R.1 E.

Primary recharge area, o unconsolidated material N 111 45' Secondary recharge area Discharge area U T A H

Water body 3036Miles

Water course 3036Kilometers

Figure 6. Recharge areas in Cache Valley, Cache County, Utah (after Anderson and others, 1994). Special Study 101 11 health-related) ground-water quality standards for chloride, McGreevy (1971) attributed elevated TDS to irrigation and fluoride, iron, nitrate, and sulfate (Beer, 1967; Bjorklund and drainage practices. One sample from a 24-foot-deep (7 m) McGreevy, 1971); we did not analyze for fluoride in our well completed in the shallow unconfined aquifer at a mink study. ranch west of Nibley yielded ground water with a TDS concentration of 1,236 mg/L (not shown on plate 1). GROUND-WATER QUALITY Plate 2 shows the distribution of TDS with respect to perforated-interval category and hydrogeologic setting CLASSIFICATION (recharge/discharge area category). Of the 163 wells sampled and analyzed for TDS, 37 are shallow wells (less than Introduction 100 feet [30 m] deep) completed in the principal aquifer, (2) 79 are medium-depth wells (100-200 feet [30-60 m] deep) Ground-water quality classification, based primarily on completed in the principal aquifer, (3) 42 are deep wells TDS (table 1), is a tool for local governments in Utah to use (greater than 200 feet [60 m] deep) completed in the princi- for managing potential ground-water contamination sources pal aquifer, and (4) one well and the spring are in and asso- and for protecting the quality of their ground-water ciated with the shallow unconfined aquifer. The determina- resources. The Utah Division of Water Quality’s (1998) tion that these sampled wells are completed in unconsolidat- Aquifer Classification Guidance Document and Lowe and ed basin-fill deposits is based on drillers’ logs of water wells; Wallace (1999a, b) outline why ground-water quality classi- in some instances Tertiary semiconsolidated rock may have fication exists, what is required to classify ground-water been logged as unconsolidated deposits. Depth is not known quality, and why ground-water quality classification should for five of the sampled wells presumed to be completed in be considered as a tool to protect ground-water quality. Basi- the principal aquifer. Average TDS is 468 mg/L for water cally, it is one way to implement an anti-degradation ap- from deep wells, 327 mg/L for water from medium-depth proach for managing ground-water resources using differen- wells, and 390 mg/L for water from shallow wells complet- tial protection based on the quality or value of the ground- ed in the principal aquifer. Average TDS for water from the water resource. The policy of differential protection recog- wells for which we have no depth information, typically nizes possible impacts on ground water from human activi- older wells drilled or dug before well logs were required, is ties, but limits any adverse impacts to pre-established accept- 845 mg/L. The spring (not shown on plates 1 and 2) yielded able levels tied directly to the existing ground-water quality. water with a TDS concentration of 368 mg/L. Figure 7 sum- Ground-water quality classification is one of the principal marizes the percentage of wells in each perforated-depth means for implementing the differential protection policy interval category that are above or below 500 mg/L TDS. because it establishes the quality of the ground-water re- Figure 8 shows the non-linear relationship between TDS and source. On behalf of Cache County, we petitioned the Utah perforated-interval depth; the correlation coefficient is 0.56, Water Quality Board for formal classification of the principal an indication that no strong statistical correlation exists aquifer in Cache Valley; based on that petition the Utah between TDS and perforated-interval depth. Note that TDS Water Quality Board formally adopted the ground-water in ground water in many of the wells with deeper perforated quality classification as presented in this report on August intervals is greater than 500 mg/L (figures 7a,b and 8); this 10, 2001. pattern is especially prevalent in ground-water-discharge areas (figure 7b), and may be due to longer ground-water res- Results idence times and/or flow paths than ground water in wells with shallower perforated intervals. Total-Dissolved-Solids Concentrations With respect to hydrogeologic setting (plate 2), of the 163 wells sampled and analyzed for TDS, three are in pri- The Utah Water Quality Board’s drinking-water quality mary recharge areas (15 percent of the surface area of basin- (health) standard for TDS is 2,000 mg/L for public-supply fill deposits), 42 are in secondary recharge areas (22 percent wells (table A.1). The secondary ground-water quality stan- of the surface area of basin-fill deposits), and 118 are in dis- dard is 500 mg/L (U.S. Environmental Protection Agency, charge areas (63 percent of the surface area of basin-fill 2002) (table A.1), and is primarily due to potential adverse deposits) based on the recharge-area map of Anderson and impacts on the taste of the water (Bjorklund and McGreevy, others (1994). For ground water from primary-recharge-area 1971). Plate 1 shows the distribution of TDS in Cache Val- wells, TDS ranges from 358 to 828 mg/L and averages 554 ley’s principal unconsolidated basin-fill aquifer based on our mg/L. For ground-water from secondary-recharge-area data for ground water sampled from 163 wells during fall wells, TDS ranges from 232 to 664 mg/L and averages 366 1997 and winter/spring 1998 (appendix A). Total-dissolved- mg/L. For ground water from discharge-area wells, TDS solids concentrations range from 178 to 1,758 mg/L, and ranges from 178 to 1,758 mg/L and averages 399 mg/L. Fig- average background TDS is 393 mg/L. Most of the ground ure 9 summarizes the percentage of wells in each hydrogeo- water in the principal aquifer has TDS concentrations gener- logic setting category that are above or below 500 mg/L ally less than 500 mg/L (plate 1). However, ground water in TDS; no trend is apparent with respect to hydrogeologic set- the northwestern part of Cache Valley has TDS concentra- ting and TDS, but our sampled wells are not well-distributed tions generally between 500 and 750 mg/L, and ground water with respect to each category. southwest of Amalga has TDS concentrations between 750 and 1,000 mg/L (plate 1). Three wells yielded ground-water Nitrate Concentrations samples that exceeded TDS concentrations of 1,000 mg/L. Two wells (1,468 and 1,758 mg/L TDS) of unknown depth The ground-water quality (health) standard for nitrate is are north of Lewiston, in an area where Bjorklund and 10 mg/L (table A.1) (U.S. Environmental Protection Agency, 12 Utah Geological Survey

A a. 60

20 PERCENTAGE OF WELLS PERCENTAGE 10

Water with Water with Depth of Perforations TDS less than or TDS greater Shallow (< 100 feet) equal to 500 mg/L than 500 mg/L Medium (100-200 feet) Deep (> 200 feet) B b. 60 Unknown

20 PERCENTAGE OF WELLS PERCENTAGE 10

Water with Water with TDS less than or TDS greater equal to 500 mg/L than 500 mg/L

Figure 7. Percentage of wells in shallow, medium, deep, and unknown perforation depth intervals above and below 500 mg/L total-dissolved-solids concentrations in Cache Valley, Cache County, Utah. Data for all wells are shown in a; data for discharge-area wells only are shown in b.

Figure 8. Relationship between well depth and total-dissolved-solids concentrations in Cache Valley, Cache County, Utah. Correlation coefficient is 0.56. Special Study 101 13

100

Hydrogeologic Setting 40 Primary recharge areas Secondary recharge areas

PERCENTAGE OF WELLS PERCENTAGE 20 Discharge areas

Total wells TDS concentrations TDS concentrations sampled less than or greater than equal to 500 mg/L 500 mg/L

Figure 9. Percentage of wells in each hydrogeologic setting sampled for TDS concentrations that are less than or equal to 500 mg/L and greater than 500 mg/L in Cache Valley, Cache County, Utah

2002). More than 10 mg/L of nitrate in drinking water can interval category; the correlation coefficient of -0.2 indicates result in a condition known as methoglobinemia, or “blue that no statistical correlation exists between nitrate concen- baby syndrome” (Comley, 1945) in infants under six months tration and perforated interval. and can be life threatening without immediate medical atten- With respect to hydrogeologic setting (plate 4) based on tion (U.S. Environmental Protection Agency, 2002). This the recharge-area map of Anderson and others (1994), nitrate condition is characterized by a reduced ability for blood to concentration ranges from less than 0.02 to 11.91 mg/L and carry oxygen. Nitrate-plus-nitrite concentrations in Cache averages 3.5 mg/L for ground water from primary-recharge- Valley’s principal aquifer (plate 3; appendix A) range from area wells. For ground-water from secondary-recharge-area less than 0.02 to 35.77 mg/L, with an average (background) wells, nitrate concentration ranges from less than 0.02 to nitrate concentration of 0.68 mg/L. Thirty-eight wells were 20.62 mg/L and averages 0.58 mg/L. For ground water from below the detection limit for nitrate of 0.02 mg/L (appendix discharge area wells, nitrate concentration ranges from less A) for the laboratory analysis method listed in table A.1. than 0.02 to 32.85 mg/L, and averages 1.9 mg/L. Figure 12 Seven wells, one northwest of Lewiston, two near Clarkston, summarizes the percentage of wells in each hydrogeologic- three southwest of Hyrum, and the mink ranch well with high setting category that are less than 3 mg/L nitrate concentra- TDS (not shown on plate 3), yielded water samples that tion, 3 to 10 mg/L nitrate, and greater than 10 mg/L nitrate. exceed the ground-water quality (health) standard of 10 Primary recharge areas have the highest average nitrate con- mg/L for nitrate. High nitrate levels may be attributed to centration (Wallace and Lowe, 1999a). contamination from septic-tank systems, feedlots, and/or fertilizer. Dissolved-Iron Concentrations Plate 4 shows the distribution of nitrate concentrations with respect to perforated-interval category and hydrogeo- The secondary ground-water quality standard for iron is logic setting. The distribution of wells with respect to perfo- 300 µg/L (table A.1) (U.S. Environmental Protection Ag- rated-interval category and hydrogeologic setting is as ency, 2002), primarily to avoid objectionable staining to described for TDS above. Average nitrate concentration is plumbing fixtures, other household surfaces, and laundry 0.57 mg/L for water from deep wells, 0.42 mg/L for water (Fetter, 1980; Hem, 1989). Water high in dissolved iron can from medium-depth wells, and 1.05 mg/L for water from also lead to the growth of iron bacteria which may lead to the shallow wells completed in the principal aquifer. Average clogging of water mains, recirculating systems, and, some- nitrate concentration for water from the wells for which we times, wells (Driscoll, 1986). At concentrations over 1,800 had no depth information is 6.4 mg/L. The spring (not shown µg/L, iron imparts a metallic taste to drinking water (Fetter, on plates 3 and 4) yielded water with a nitrate concentration 1980). Dissolved concentrations of iron in Cache Valley’s of 3.91 mg/L. Figure 10 summarizes the percentage of wells principal aquifer (plate 5) range from less than 20 to 7,560 in each perforated-interval category that are less than 3 mg/L µg/L, with an average (background) dissolved-iron concen- nitrate concentration, 3 to 10 mg/L nitrate, and greater than tration of 403 µg/L. A total of 82 wells yielded ground water 10 mg/L nitrate; more than 60 percent of the wells that yield that was below the detection limit for dissolved iron of 20 ground water having high-nitrate concentrations (>10 mg/L N) µg/L (appendix A) for the analysis method listed in table A.1. are either in the shallow perforated-interval category or have Forty-two wells yielded water samples that exceed the sec- unknown perforated-interval depths. Figure 11 shows the ondary ground-water quality standard for iron. relationship between nitrate concentration and perforated- Plate 5 shows the distribution of dissolved-iron concen- 14 Utah Geological Survey

40 EXPLANATION

Shallow (<100 feet) Medium (100-200 feet) 20 Deep (>100 feet) PERCENTAGE OF WELLS PERCENTAGE Unknown

0 Water with less Water with NO3 Water with10 mg/L than 3 mg/L NO 3 between 3 NO3 and greater Fig 21 Nitrate Wells & SMD Fig 21 Nitrate Wells (78% of wells) and less than 10 mg/L (4% of wells) (18% of wells) Zip#3 :

Nitrate as nitrogen concentration

Figure 10. Percentage of wells in shallow, medium, and deep perforation-depth intervals that are less than 3 mg/L, between 3 and 10 mg/L, and greater than 10 mg/L nitrate concentration in Cache Valley, Cache County, Utah.

!"! " "

Figure 11. Well depth versus nitrate concentration in Cache Valley, Cache County, Utah. Correlation coefficient is -0.2. Special Study 101 15

50 EXPLANATION 40 Primary Recharge Areas Secondary Recharge Areas 30 Discharge Areas 20 PERCENTAGE OF WELLS PERCENTAGE 10

0 Total wells Water with Water with NO3 Water with sampled less than between 3 10 mg/L NO3 3 mg/L NO3 and less than and greater 10 mg/L

Figure 12. Percentage of wells in each hydrogeologic-setting category that are less than 3 mg/L, between 3 and 10 mg/L, and 10 mg/L or greater nitrate concentration in Cache Valley, Cache County, Utah. tration with respect to perforated-interval category and (appendix A) for the analysis listed on table A.1. Only two hydrogeologic setting. Average dissolved-iron concentration wells yielded water samples that exceed the secondary is 204.5 µg/L for water from deep wells, 720.7 µg/L for ground-water quality standard for sulfate; most wells yielded water from medium-depth wells, and 597.9 µg/L for water ground water with sulfate concentrations below the detection from shallow wells completed in the principal aquifer. Fig- limit of 10 mg/L, so statistical analysis of the distribution of ure 13 shows the relationship between dissolved-iron con- sulfate concentrations with respect to perforated-interval centration and perforated-interval depth; the correlation coef- depth and hydrogeologic setting do not produce meaningful ficient is -0.1 indicating no statistical correlation exists be- results. Geologic provenance (source rock for basin-fill sed- tween dissolved-iron concentration and perforated-interval iment) likely is an important factor determining the distribu- depth. tion of sulfate in the basin-fill aquifer; metallic sulfides in With respect to hydrogeologic setting (plate 5) based on both igneous and sedimentary rocks are common sources of the mapping of Anderson and others (1994), dissolved-iron sulfur in its reduced form (Hem, 1989). concentration averages 158 µg/L for ground water from primary-recharge-area wells. For ground water from second- Chloride Concentrations ary-recharge-area wells, dissolved-iron concentration averages 494 µg/L. For ground water from discharge-area wells, The secondary ground-water quality standard for chlo- dissolved-iron concentration averages 416 µg/L. Average ride is 250 mg/L (table A.1) (U.S. Environmental Protection dissolved iron with respect to hydrogeologic setting may Agency, 2002), primarily because of the potential for its reflect longer average ground-water residence times in sec- imparting a salty taste to drinking water (Hem, 1989). Chlo- ondary recharge areas and discharge areas than in primary ride at concentrations over 500 mg/L can cause corrosion to recharge areas. Geologic provenance (source rock for basin- wells and plumbing (Driscoll, 1986). Dissolved concentra- fill sediment) likely is an important factor determining the tions of chloride in Cache Valley’s principal aquifer (plate 7) distribution of dissolved iron in the basin-fill aquifer; for range from less than 3 to 515 mg/L, with an average (back- example, igneous rocks containing abundant pyroxene, ground) chloride concentration of 52 mg/L. Only one well amphibole, biotite, magnetite, and especially fayalite (iron yielded ground water below the detection limit for chloride olivine), have high iron content. of 3 mg/L (appendix A) for the analysis method listed in table A.1. Nine wells yielded water samples that exceed the sec- Sulfate Concentrations ondary ground-water quality standard for chloride. Plate 7 shows the distribution of chloride concentration The secondary ground-water quality standard for sulfate with respect to perforated-interval category and hydrogeo- is 250 mg/L (table A.1) (U.S. Environmental Protection logic setting. The distribution of wells with respect to perfo- Agency, 2002), primarily because of odor/taste problems and rated-interval category and hydrogeologic setting is as because high-sulfate water can have a laxative effect (Fetter, described for TDS above. Average chloride concentration is 1980). Dissolved concentrations of sulfate in Cache Valley’s 120 mg/L for water from deep wells, 20 mg/L for water from principal aquifer (plate 6) range from less than 10 to 305 medium-depth wells, and 27 mg/L for water from shallow mg/L, with an average (background) sulfate concentration of wells completed in the principal aquifer. Figure 14 shows the 21 mg/L. A total of eighty-seven wells yielded ground water relationship between chloride concentration and perforated- that was below the detection limit for sulfate of 10 mg/L interval depth; the correlation coefficient is 0.7 indicating a 16 Utah Geological Survey weak statistical correlation exists between chloride concen- cycle sediments, and previous deep-lake-cycle sediments, tration and perforated-interval depth. This weak correlation make up much of the basin fill in Cache Valley and could may be due to longer ground-water residence time for water also be sources of chloride. samples from deep wells. With respect to hydrogeologic setting (plate 7) based on Other Constituents the map of Anderson and others (1994), dissolved-chloride concentration averages 53 mg/L for ground water from pri- A water sample from one well near the confluence of the mary-recharge-area wells, 28 mg/L for ground water from Little Bear River and the Bear River yielded an arsenic value secondary-recharge-area wells, and 60 mg/L for ground of 100 µg/L, twice the ground-water quality standard of 50 water from discharge-area wells. Geologic provenance µg/L. Gross alpha is below 5 pCi/L for all ground-water sam- (source rock for basin-fill sediment) likely is an important ples, so samples were not analyzed subsequently for specific factor determining the distribution of chloride in the basin- radionuclides. Of water wells tested for pesticides, only one fill aquifer; although chloride is present at low concentra- well yielded water with a value above the detection limit for tions in many rock types it is more common in sedimentary atrazine, but the value was less than the upper limit for rocks, especially evaporites (Hem, 1989). Bonneville lake- ground-water quality standards.

Figure 13. Iron concentration versus well depth in Cache Valley, Cache County, Utah. Correlation coefficient is -0.1.

$ "%"! " "!

Figure 14. Chloride concentration versus well depth in Cache Valley, Cache County, Utah. Correlation coefficient is 0.7.

% !"! " " Special Study 101 17

Resulting Ground-Water Quality Classification been monitored at locations associated with leaking underground storage tanks by Ecosystems Research Institute The ground-water quality classification shown on plate 8 (1996). is based on the data from the 163 wells completed in the principal aquifer which were sampled between fall and win- Possible land-use-planning applications of this ground- ter of 1997-98 and spring of 1998 by the Utah Division of water quality classification: Ground-water quality classifi- Environmental Quality. Some areas, where insufficient data cation is a tool that can be used in Utah to manage potential exist, require extrapolation of ground-water quality condi- ground-water contamination sources and protect the quality tions. The basis for our extrapolation was local geologic of ground-water resources. As such, the wide range of land- characteristics. The ground-water quality classes are as fol- use-planning applications of this tool have not been fully lows: explored. Ground-water quality classification has been used Class IA - Pristine ground water: For this class, TDS con- in Heber Valley in Wasatch County and Ogden Valley in centrations in Cache Valley range from 178 to 492 mg/L. Weber County, in concert with septic-tank density/water- Class IA is the predominant ground-water quality class in quality-degradation studies (Hansen, Allen, and Luce, Inc., Cache Valley (plate 8). Areas having Pristine ground water 1984; Wallace and Lowe, 1998, 1999), to establish minimum cover about 84 percent of the total basin-fill material. lot sizes where septic-tank systems are used for wastewater disposal. Class II - Drinking Water Quality ground water: For this class, TDS concentrations in Cache Valley range from 504 to Using ground-water quality classification in conjunction 1,758 mg/L. Class II areas are present in the northern, north- with the septic-tank density/water-quality degradation analy- western, central, and southern parts of the valley in Utah sis presented below to set maximum densities for develop- (plate 8). The areas having Drinking Water Quality ground ment using septic-tank systems for wastewater disposal in water cover about 16 percent of the total basin-fill material. Cache Valley is one possible application of the ground-water quality classification presented above. Additional potential Class III - Limited Use ground water: For this class, no uses include using ground-water quality classification as a TDS values between 3,000 and 10,000 mg/L were identified. basis for prohibiting the dumping of poor-quality water and However, water from the seven wells completed in the principal aquifer that exceed ground-water quality standards (one other liquid or solid wastes into poorly lined or unlined arsenic, six nitrate) is considered Limited Use ground water. canals, especially in vulnerable ground-water recharge areas. These wells could not be mapped as a discrete Class III area Ground-water quality classification can also be used to due to their sporadic distribution. enhance restrictions on the siting of new potential pollution sources in drinking-water source-protection zones 1 and 2 for public water-supply wells. Land-Use Planning Considerations

Current beneficial uses of ground water: Ground water, most of which is from the basin-fill aquifer, is the most SEPTIC-TANK DENSITY/WATER-QUALITY important source of drinking water in Cache Valley. The DEGRADATION ANALYSIS results of the ground-water quality classification for Cache Valley indicate that the basin-fill aquifer contains mostly Introduction high-quality ground-water resources that warrant protection. According to Steiger and others (1996), ground-water use in Land-use planners have long used septic-tank-suitability Cache Valley is as follows: 54 percent for irrigation, 19 per- maps to determine where these systems will likely percolate cent for public supply, 19 percent for industry, and 8 percent within an acceptable range. However, percolation alone does for domestic and stock-watering purposes. There are 3,018 not remediate many constituents found in wastewater, perfected water wells in Cache Valley, 60 of which are pub- including nitrate. Ammonium from septic-tank effluent un- lic-supply wells. der aerobic conditions can convert to nitrate, contaminating Potential for ground-water quality degradation: Potential ground water and posing potential health risks to humans contaminant sources in Cache Valley include underground (primarily very young infants) (Comley, 1945). The U.S. storage tanks, leaking underground storage tanks, confined Environmental Protection Agency’s maximum contaminant animal-feeding operations, areas served by public sewer sys- level for nitrate in drinking water (Utah ground-water quali- tems, lagoons, landfills, rapidly developing areas with septic ty standard) is 10 mg/L. With continued population growth systems, and fertilizer distributors. Although the actual and installation of septic tank soil-absorption systems in new potential of contamination from these potential sources developments, the potential for nitrate contamination will ranges from negligible to nearly certain (for instance, septic increase. One way to evaluate the potential impact of septic- tanks), they do indicate that there is a potential for degrada- tank systems on ground-water quality is to perform a mass- tion of Cache Valley’s valuable and mostly pristine ground- balance calculation (Hansen, Allen, and Luce, Inc., 1994; water resources. Zhan and McKay, 1998; Lowe and Wallace, 1999c, d; Wal- Some ground-water quality degradation has already been lace and Lowe, 1998a, b, c, 1999b; Lowe and others, 2000). documented. Approximately 600 underground storage tanks This type of analysis may be used as a gross model for eval- were identified in Cache County, 51 of which were catego- uating the possible impact of proposed developments using rized as leaking underground storage tanks (Ecosystems septic-tank systems for wastewater disposal on ground-water Research Institute, 1996). Twenty-five of the 51 tanks have quality and allowing planners to more effectively determine since been closed. Petroleum hydrocarbon (TPH) leaks have appropriate average septic-system densities. 18 Utah Geological Survey

Ground-Water Contamination from they volatilize easily, are not remediated by percolation Septic-Tank Systems through soils in the unsaturated zone. Contamination from these chemicals can be minimized by reducing their disposal Pathogens via septic-tank systems, maximizing the potential for dilution of those chemicals that do reach ground water via septic As the effluent from a septic tank soil-absorption system tanks (Lowe and Wallace, 1999e). leaves the drain field and percolates into the underlying soil, it can have high concentrations of pathogens, such as viruses Phosphate and bacteria. Organisms such as bacteria can be mechani- Phosphate, typically derived from organic material or cally filtered by fine-grained soils and are typically removed some detergents, is discharged from septic-tank systems after traveling a relatively short distance in the unsaturated (Fetter, 1980). While phosphate (and phosphorus) is a major zone. However, in coarse-grained soils, or soils containing factor in causing eutrophication of surface waters (Fetter, preferential flow paths like cracks, worm burrows, or root 1980), it is generally not associated with water-quality degra- holes, these pathogens can reach the water table. Pathogens dation due to the use of septic-tank systems (Lowe and Wal- can travel up to 40 feet (12 m) in the unsaturated zone in lace, 1999e). Phosphates are removed from septic-tank sys- some soils (Franks, 1972). Some viruses can survive up to tem effluent by absorption onto fine-grained soil particles 250 days (U.S. Environmental Protection Agency, 1987), and by precipitation with calcium and iron (Fetter, 1980). In which is the minimum ground-water time of travel for public most soils, complete removal of phosphate is common (Franks, water-supply wells or springs to be separated from potential 1972). biological contamination sources. Nitrate Household and Industrial Chemicals Ammonia and organic nitrogen are commonly present in Many household and industrial chemicals (table 3) are effluent from septic-tank systems (table 3), mostly from the commonly disposed of through septic systems and, unless human urinary system. Typically, almost all ammonia is con-

Table 3. Typical characteristics of wastewater from septic-tank systems (from Hansen, Allen, and Luce, Inc., 1994). Parameter Units Quantity Total Solids mg/L 680 - 1000 Volatile Solids mg/L 380 - 500 Suspended Solids mg/L 200 - 290 Volatile Suspended Solids mg/L 150 - 240 BOD mg/L 200 - 290 Chemical Oxygen Demand mg/L 680 - 730 Total Nitrogen mg/L 35 - 170 Ammonia mg/L 6 - 160 Nitrites and Nitrates mg/L <1 Total Phosphorus mg/L 18 - 29 Phosphate mg/L 6 - 24 Total Coliforms **MPN/100#mL 1010 - 1012 Fecal Coliforms **MPN/100#mL 108 - 1010 pH - 7.2 - 8.5 Chlorides mg/L 86 - 128 Sulfates mg/L 23 - 48 Iron mg/L 0.26 - 3.0 Sodium mg/L 96 - 110 Alkalinity mg/L 580 - 775 P-Dichlorobenzene* mg/L 0.0039 Toluene* mg/L 0.0200 1,1,1-Trichloroethane* mg/L 0.0019 Xylene* mg/L 0.0028 Ethylbenzene* mg/L 0.004 Benzene* mg/L 0.005

* Volatile Organics are the maximum concentrations ** Most probable number Special Study 101 19 verted into nitrate before leaving the septic tank soil-absorp- 1997), was determined using the ground-water flow model of tion system drain field. Once nitrate passes below the zone Kariya and others (1994). of aerobic bacteria and the roots of plants, there is negligible attenuation as it travels farther through the soil (Franks, Limitations 1972). Once in ground water, nitrate becomes mobile and There are many limitations to any mass-balance ap- can persist in the environment for long periods of time. proach (see, for example, Zhan and McKay [1998]; Wallace Areas having high densities of septic-tank systems risk ele- and Lowe, 1998a, b, c, 1999b). We identify the following vated nitrate concentrations reaching unacceptable levels. In limitations to our application of the mass-balance approach: the early phases of ground-water quality degradation associated with septic-tank systems, nitrate is likely to be the only 1. Calculations are typically based on a short-term pollutant detected (Deese, 1986). Regional nitrate contami- hydrologic budget, a limited number of aquifer nation from septic-tank discharge has been documented on tests, and limited water-gradient data. Long Island, New York, where many densely populated areas 2. Background nitrate concentration is attributed to without sewer systems have existed (Fetter, 1980). natural sources, agricultural practices, and use of A typical single-family septic-tank system in Cache Val- septic-tank systems, but projected nitrate concen- ley discharges about 227 gallons (859 L) of effluent per day trations are based on septic-tank systems only and containing nitrate concentrations of around 55 mg/L; see dis- do not include nitrate from other potential sources (such as lawn and garden fertilizer). cussion below. The U.S. Environmental Protection Agency 3. Calculations do not account for localized, high- (2002) maximum contaminant level for nitrate in drinking concentration nitrate plumes associated with indi- water (ground-water-quality [health] standard) is 10 mg/L. vidual or clustered septic-tank systems, and also Therefore, distances between septic tank soil-absorption sys- assumes that the septic-tank effluent from exist- tem drain fields and sources of culinary water must be suffi- ing homes is in a steady-state condition with the cient for dilution of nitrate in the effluent to levels below the aquifer. ground-water quality standard. 4. The approach assumes negligible denitrification. We consider nitrate to be the key contaminant for use in 5. The approach assumes uniform, instantaneous determining the number or density of septic-tank systems ground-water mixing for the entire aquifer or that should be allowed in Cache Valley. Projected nitrate entire mixing zone below the site. 6. Calculations do not account for changes in concentrations in all or parts of aquifers can be estimated for ground-water conditions due to ground-water increasing septic-tank-system densities using a mass-balance withdrawal from wells (see ground-water dis- approach. charge section above). 7. Calculations are based on aquifer parameters that The Mass-Balance Approach must be extrapolated to larger areas where they may not be entirely representative. General Methods 8. Calculations may be based on existing data that do not represent the entire valley. We use a mass-balance approach for water-quality degradation assessments because it is easily applied, requires Although there are many caveats to applying this mass- few data, and provides a quantitative basis for land-use plan- balance approach, we think that it is useful in land-use planning decisions. In the mass-balance approach to compute ning because it provides a general basis for making recom- projected nitrate concentrations, the average nitrogen mass mendations for septic-tank-system densities. In addition, the expected from projected new septic tanks is added to the approach is cost-effective and easily applied with limited in- existing, ambient (background) mass of nitrogen in ground formation. water and then diluted with the known (or estimated) ground- water flow available for mixing, plus water that is added to Ground-Water Flow Calculations the system by septic tanks. We used a discharge of 227 gallons (859 L) of effluent per day for a domestic home based Introduction on a per capita indoor usage of 70 gallons (265 L) per day (Utah Division of Water Resources, 2001a, p. 28; 2001b, p. We used the GMS (Boss International, Inc. and Brigham 83-106) by Cache County’s average 3.24 person household Young University, 1999) ground-water modeling system, (U.S.Census Bureau, 2002). We used an estimated nitrogen applied to the regional, three-dimensional, steady-state loading of 55 mg/L of effluent per domestic septic tank based MODFLOW (McDonal and Harbaugh, 1988) model of on: (1) an average of 3.24 people per household, (2) an aver- Kariya and others (1994), to determine the available ground- age nitrogen loading of 17 g N per capita per day (Kaplan, water flow in the upper portion of saturated, unconsolidated 1988, p. 149), and (3) an assumed retainment of 15 percent basin-fill deposits of the principal aquifer in the Utah portion of the nitrogen in the septic tank (to be later removed during of Cache Valley. The model simulated confined and uncon- pumping) (Andreoli and others, 1979, in Kaplan, 1988, p. fined conditions, withdrawal from wells, evapotranspiration, 148); this number is close to Bauman and Schafer’s (1985, in seepage to and from streams, areal recharge, seepage to Kaplan, 1988, p. 147) nitrogen concentration in septic-tank drains, and seepage from consolidated rock. effluent of 62 ± 21 mg/L based on the averaged means from Computer Modeling 20 previous studies. Ground-water flow available for mixing, the major control on nitrate concentration in aquifers We used Kariya and others’ (1994) three-dimensional, when using the mass-balance approach (Lowe and Wallace, finite-difference, numerical MODFLOW model (McDonald 20 Utah Geological Survey and Harbaugh, 1988) of ground-water flow for the basin-fill six were computed by multiplying the estimated hydraulic- aquifer system in Cache Valley to provide cell-by-cell flow conductivity values for layer one by the thickness of each data under steady-state conditions. We apply Kariya and oth- layer. During the steady-state calibration of the model, input ers’ (1994) model as it provides the best representation cur- parameters were systematically varied and refined to a non- rently available of the Cache Valley basin-fill aquifer, but uniform distribution. The final distribution of transmissivity Kariya and others (1994, p. 58) point out that “a ground- values for layers two through four can be obtained by multi- water model is a tool to simulate a simplified version of a plying the final hydraulic conductivity of layer one by the ground-water system,” and we acknowledge this tool may be thickness of the layer in question. During calibration, trans- improved upon by future investigators. For steady-state con- missivity values in layers five and six were reduced to the ditions, the model is constructed to represent a ground-water value for layer four to be more consistent with aquifer-test flow system in which there is no change in storage or long- data. For layer one, to achieve a best fit between simulated term water levels – in other words, recharge and discharge and observed data the final values of hydraulic conductivity from the system are exactly equal. Kariya and others’ (1994) for the calibrated model ranged from 1 to 100 feet per day model was calibrated to assumed 1969 steady-state condi- (0.3-31 m/d). Transmissivity values used in the calibrated tions, a year having the best available ground- and surface- model for layers two to four range from 100 to 18,000 square water data. feet per day (9-1,672 m2/d). The steady-state simulation assumes the water flowing into the ground-water system Description of model of Kariya and others (1994) equals the amount flowing out, with no change in ground- water storage. The vertical leakage used to represent confin- Kariya and others (1994) used the U.S. Geological Sur- ing units in the model were calculated based on the vertical vey modular three-dimensional, finite-difference, ground- hydraulic conductivity determined by comparing simulated water flow simulator (MODFLOW) (McDonald and Har- vertical-head differences between layers. Cells in layer one baugh, 1988) to test and refine their conceptual understand- with spring discharge are assigned an increased vertical con- ing of the flow system in Cache Valley. The area covered by ductance. the saturated unconsolidated basin-fill deposits was dis- Boundary conditions for the Cache Valley model were cretized into a non-uniform, horizontal, quasi-three-dimensional, rectangular grid consisting of 82 rows and 39 based on a simplified hydrologic model. Kariya and others columns, with up to six vertical layers of cells. The grid rep- (1994) specified the lateral boundaries surrounding the active resents an area smaller than the actual area of unconsolidat- cells of the model as “no-flow” boundaries by assuming they ed basin-fill because some deposits are not saturated. The coincided with low-permeability bedrock, except where model uses a vertical leakage term between the six vertical inflow from adjacent consolidated rock or unconsolidated model layers, and assumes two-dimensional horizontal flow basin-fill deposits was identified during the calibration of the in the aquifer and one-dimensional vertical flow. model. To simulate subsurface inflow into the main ground- The model’s rectilinear grid has a grid-cell spacing rang- water system of Cache Valley, general-head cells were used ing from 0.5 miles (0.8 km) by 0.375 miles (0.6 km) to 1 mile at the boundary of layer one. The upper boundary of the (1.6 km) on each side, resulting in cell areas of 0.2 to 1 model is a specified-flux boundary formed by using square mile (0.5-2.6 km2). The y-axis of the model is ori- recharge, well, evapotranspiration, river, and drain packages ented north-south, parallel to the axis of the valley and the of MODFLOW to simulate the infiltration and discharge of primary surface-water drainages. Activity cells in layers one ground water. The lower boundary of the model is a no-flow and two represent an area of approximately 660 square miles boundary. (1,789 km2), with 282 square miles (730 km2) in Utah. In the model, recharge of the Cache Valley basin-fill Layer one was simulated as an unconfined layer with an ini- aquifer occurs: (1) where infiltration of unconsumed irriga- tial saturated thickness of 100 feet (30 m), with changes in tion water and precipitation occurs, (2) where perennial the water levels causing the saturated thickness to vary from streams emerge from canyons, or canals flow across coarse- the initial 100 feet (30 m); within the basin-fill deposits rep- grained deposits along the margins of the valley, allowing resented by this layer, confined conditions may occur in water to infiltrate readily to the underlying ground-water sys- some areas. Layer one simulates evapotranspiration, dis- tem, and (3) from subsurface inflow. Alluvial fans and deltas charge from wells and springs, and seepage to streams, adjacent to the Bear River Range are important recharge rivers, and a reservoir. Layer two simulates saturated valley- areas. Twelve perennial streams enter the valley and flow fill material from 100 to 200 feet (30-61 m) using a confined- toward the Bear River; ten of these are from the Bear River or unconfined-layer option that allows the storage term to be Range and three are from mountains on the west side of the converted from confined to unconfined in cells when calcu- valley. These tributaries contribute to the surface and sub- lated water levels drop below the top of the cell. Layers three surface water supplies. Before the time of large-scale irriga- through six were simulated using the confined-layer option. tion, infiltration from streams flowing across the alluvial fans The depth of saturated basin-fill deposits simulated by layer and deltas was probably the main source of ground water; three is from 200 to 300 feet (61-91 m), layer four from 300 now, the infiltration of unconsumed irrigation water is almost to 500 feet (91-152 m), layer five from 500 to 1,000 feet as important (Kariya and others, 1994). Estimated recharge (152-305 m), and layer six from 1,000 to 1,500 feet (305-457 over the modeled area of Cache Valley is 326,000 acre-feet m). Layer six allows simulation of pumping from deep per year (402 km3/yr) (Kariya and others, 1994). Ground- municipal wells in the eastern part of the valley. water discharge in Cache Valley is primarily from: (1) seep- Kariya and others (1994) initially estimated hydraulic age to the Bear, Cub, Logan, Blacksmith Fork, and Little parameters based on single-well specific-capacity tests for Bear Rivers, (2) evapotranspiration in the marshes and wet- layer one. Initial transmissivity values of layers two through lands, and (3) withdrawals from wells and springs. The Special Study 101 21 largest component of ground-water discharge in Cache Val- ley is seepage to rivers; the net gain to flow in the Bear River Table 4. Cities/towns and land area within each ground-water (including Cutler Reservoir) from seepage between Smith- flow domain (plate 9) in Cache Valley, Cache County, Utah. field and the Box Elder county line was 79 cubic feet per sec- Domain Area Cities/towns ond (2.2 m3/sec) (Herbert and Thomas, 1992). Estimated (square discharge over the modeled area of Cache Valley is 325,000 miles) acre-feet per year (400 km3/yr) (Kariya and others, 1994), The model of Kariya and others (1994) did not simulate 1 14.2 Cove the approximately 45.5-square-mile (118 km2) Clarkston 2 31.2 Lewiston Bench area, because this area has its own individual basin- 3 9.8 Cornish fill ground-water system and is at a higher altitude than the 4 45.5 Clarkston, Newton ground-water system in Cache Valley. Consolidated rocks are at shallower depths in the Clarkston Bench area and the 5 39.3 Richmond, Trenton, Amalga unconsolidated basin fill is thin (about 20 feet [6 m] thick, on 6 33.3 Benson average). Little is known of the thickness or extent of water- 7 18.4 Smithfield, Hyde Park bearing material in the Clarkston Bench area. We considered the water table in the shallow sediments to be approximately 8 22.6 Petersboro the same as the unconsolidated basin-fill topography. Sand 9 19.0 Mendon and gravel deposits yield water to a few wells in the Clark- 10 61.2 Young Ward, Nibley, College ston Bench area. Multiplying the volume of the unconsoli- Ward, Wellsville dated basin-fill deposits by the average specific yield of sed- 11 16.6 Mount Sterling iments (0.25) such as those penetrated in the Clarkston Bench area yielded an amount of water available in the sys- 12 16.5 South Hyrum, Paradise, Avon tem (52.6 cubic feet per second [1.5 m3/s]) . The available water was then evaluated over the average thickness and width of the basin-fill deposits. numerical model of a natural hydrogeologic system. Some of these assumptions limit the scope of application of the Results model and the hydrologic questions that can reasonably be addressed, and may influence the model results. The numer- The ground-water flow model used for this study is the ical model is a simplified and idealized approximation of the best available tool to qualitatively determine the available actual ground-water flow system. Kariya and others (1994) water for mixing with septic-tank effluent. Use of the simu- summarized the major simplifying assumptions and their lation improved our understanding of the aquifer system and limitations on the regional ground-water flow model. The provided the volumetric flow budget needed for the septic- model assumed a small ground-water inflow at the valley tank mass-balance calculations. The model simulation pro- margins, a layer-cake geology, and leaky aquitards through- vided a ground-water flow budget for the aquifer in relation out the basin; however, recent work by Oaks (2000) ques- to aquifer characteristics, waters in storage, and volumes and tions the validity of these assumption and their affect on rates of inflow and outflow. We used model-calculated cell- ground-water flow in the model. We used a steady-state sim- by-cell flows in this study to identify areas with similar flows ulation with time-averaged and measured conditions; thus, of water in layer one; we assume mixing/dilution of septic- the model cannot predict the transient response of the sys- tank effluent will occur within ground water modeled by this tem, because it is not calibrated to transient conditions. This layer. means we cannot use the model to predict flows in the sys- Based on the spatial distribution of the cell-by-cell flow tem if new stresses were applied, such as adding a large well, terms calculated by MODFLOW, we identified 11 regions in to the system. The model, however, can simulate steady- the Utah portion of Cache Valley with similar flows in layer state conditions and be used to evaluate various ground- one. We then used the MODFLOW flow budget for each water conditions. region to determine the available ground-water flow or volumetric flows in saturated unconsolidated basin-fill deposits for the unconfined aquifer in the Utah portion of Cache Val- Septic-Tank-System/Water-Quality- ley for each region. These regions, which we designated as Degradation Analyses domains, vary in area from 9.8 to 61.2 square miles (25-158 km2) (table 4) and have volumetric flows from 33.2 to 398.4 Introduction cubic feet per second (0.9-11 m3/sec) (table 5). We use the volumetric flows in the mass-balance calculations as the We calculated projected domain-specific nitrate concen- ground water available for mixing. Ground-water flow in the trations in the 12 ground-water flow domains (table 4, plate Clarkston Bench area, not evaluated in the model, was esti- 9) by applying a mass-balance approach using domain-spe- mated as described above; the Clarkston Bench area was des- cific parameters such as the existing nitrogen load (back- ignated as a separate ground-water flow domain, for a total ground nitrate concentration) and amount of ground water of 12 domains (plate 9). available for mixing (flow volume; table 5), and our estimated 227 gallons per day (859 L/d) contributed by each septic- Modeling Limitations tank system with a estimated nitrogen loading of 55 mg/L of septic-tank effluent. The mass-balance approach predicts the Simplifying assumptions are required to construct a impact of nitrate from use of septic-tank systems over a 22 Utah Geological Survey

Table 5. Parameters used to perform a mass-balance analysis for each ground-water flow domain in Cache Valley, Cache County, Utah. Domain Area Flow* Average nitrate Number of wells Curent number of (acres) (cubic feet concentration sampled septic tanks+ per second) (mg/L) 1 9,086 26.6 0.74 5 100 2 19,956 40.4 5.47 4 300 3 6,245 33.2 0.8 2 110 4 29,138 52.6 2.72 5 530 5 25,167 108.0 3.01 5 500 6 21,291 47.0 0.73 17 190 7 11,756 66.7 0.3 25 200 8 14,453 67.5 0.09 4 100 9 12,130 58.8 0.92 7 250 10 39,169 398.4 0.35 62 800 11 10,625 91.0 6.58 12 100 12 10,528 99.3 0.63 14 400

* ground-water flow available for mixing; data were derived using ground-water computer model, except domain 4 (Clarkston Bench area; see text for explanation). + septic systems were estimated by the Bear River Health Department (Nick Galloway, in 2001); we used 227 gallons per household as the amount of water generated based on the 2001 Utah State Water Plan (Utah Division of Water Resources, 2001).

defined area. tain an overall nitrate concentration of 1.74 mg/L (which We calculated one graph for each area based on a range allows 1 mg/L of degradation, a value adopted by Wasatch of parameters that affect the amount of ground water avail- and Weber Counties as an acceptable level of degradation), able for dilution. We obtained the number of septic-tank sys- the total number of homes using septic tank soil-absorption tems in each area from the Bear River Health Department systems should not exceed 1,525 based on the estimated (Nick Galloway, written communication, 2001). Table 5 lists nitrogen load of 55 mg/L per septic-tank system (figure 15a, the number of septic-tank systems estimated for each do- table 6). This corresponds to a total increase of approxi- main. The total number of septic-tank systems in the valley mately 1,425 septic systems and an average septic-system currently is approximately 3,580 for all the domains, and density of about 0.17 systems per acre (0.07 systems/hm2), ranges from a low of about 100 (domains 1 and 11) to a high or 6 acres per system (2.4 hm2/system) in domain 1 (table 6). of about 800 (domain 10) (table 5). Background nitrate con- Domain 4. Figure 15d shows a plot of projected nitrate concentration for each area ranges from 0.09 mg/L (domain 8) to centration versus septic-tank density and number of septic- 6.58 mg/L (domain 11). tank systems in domain 4 (Clarkston Bench area; figure 16) in northwesternmost Cache Valley (plate 9). Domain 4 dif- Results fers from the rest of the domains because this area was not included in the ground-water model, so we calculated the We herein present written descriptions of our mass-bal- amount of ground-water flow available for mixing based on ance calculations for only domains 1 (figure 15a) and 4 (fig- volume of basin-fill deposits and specific yield of sediments ure 15d) (figure 16). Calculations for domains 2, 3, and 5 of the type found in the basin-fill deposits in domain 4 as through 12 were calculated in the same manner as domain 1, described in the section on “Description of model of Kariya using the information on tables 4, 5, and 6 and figures 15b, and others (1994).” Background nitrate concentration for 15c, and 15e through 15l. domain 4 is 2.72 mg/L. Approximately 530 septic systems Domain 1. Figure 15a shows a plot of projected nitrate con- are located in domain 4 (Bear River Public Health Depart- centration versus septic-tank density and number of septic- ment, written communication, 2001). Domain 4 has an area tank systems in domain 1 (figure 16) in northeastern Cache of approximately 29,138 acres (117.9 km2), so the average Valley (plate 9). Background nitrate concentration for do- septic-system density is 0.018 systems per acre (0.007 sys- main 1 is 0.74 mg/L. Approximately 100 septic systems are tems/hm2), or 55 acres per system (22 hm2/system). Based in domain 1 (Nick Galloway, Bear River Public Health De- on our analyses (table 7), estimated ground-water flow avail- partment, written communication, 2001). Domain 1 has an able for mixing in domain 4 is 52.6 cubic feet per second (1.5 area of approximately 9,086 acres (3,677 hm2), so the exist- m3/s). For the domain 4 area to maintain an overall nitrate ing average septic-system density is 0.011 systems per acre concentration of 3.72 mg/L, the total number of homes using (0.005 systems/hm2), or 91 acres per system (37 hm2/sys- septic tank soil-absorption systems should not exceed 3,450 tem). Based on our analyses (table 7), estimated ground- based on the estimated nitrogen load of 55 mg/L per septic- water flow available for mixing in domain 1 is 26.6 cubic tank system (figure 15d). This corresponds to a total in- feet per second (0.76 m3/s). For the domain 1 area to main- crease of approximately 2,920 septic systems and an average Special Study 101 23

Septic tank density (acres/system) Septic tank density (acres/system) 7.5 9 6 67 6 10

5.5 9 5 N load 55 8 4.5 7 4 6 3.5 3 N load 55 5 background nitrate=5.47 mg/L 2.5 4 2 3 Nitrate concentration (mg/L) Nitrate concentration (mg/L) 1.5 2 1 1 0.5 background nitrate=0.74 mg/L 0 0 0 200 400 600 800 1000 1200 1400 1600 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 Number of septic tanks Number of septic tanks Figure 15a. Projected septic-tank density versus nitrate concentration Figure 15b. Projected septic-tank density versus nitrate concentration for domain 1 (table 4) in Cache Valley, Cache County, Utah, based on for domain 2 (table 4) in Cache Valley, Cache County, Utah, based on 100 existing septic tanks (see table 5). N load 55 refers to an estimat- 300 existing septic tanks (see table 5). N load 55 refers to an estimated nitrate loading per liter of wastewater from septic-tank systems (see ed nitrate loading per liter of wastewater from septic-tank systems (see text for explanation). text for explanation).

Septic tank density (acres/system) Septic tank density (acres/system) 57 3.2 6 55 8.4 7 5.5 6.5 5 6 N load 55 4.5 5.5 5 4 4.5 3.5 N load 55 4 3 3.5 2.5 3 2.5 2 background nitrate=2.72 mg/L 2 Nitrate concentration (mg/L) 1.5 Nitrate concentration (mg/L) 1.5 1 1

0.5 background nitrate=0.8 mg/L 0.5 0 0 0 200 400 600 800 1000 1200 1400 1600 1800 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 Number of septic tanks Number of septic tanks FigureFigure 15c. 15c. Projected septic-tank septic-tank density versus nitrate density concentration versus for domain nitrate 3 (table 4) concentrationin Cache Valley, Cache Figure 15d. Projected septic-tank density versus nitrate concentration for domain 3 (table 4) in Cache Valley, Cache County, Utah, based on for domain 4 (table 4) in Cache Valley, Cache County, Utah, based on 110 existing septic tanks (see table 5). N load 55 refers to an estimat- 530 existing septic tanks (see table 5). N load 55 refers to an estimated nitrate loading per liter of wastewater from septic-tank systems (see ed nitrate loading per liter of wastewater from septic-tank systems (see text for explanation). text for explanation).

Septic tank density (acres/system) Septic tank density (acres/system) 112 7.9 50 3.8 7 7 6.5 6.5 6 6 5.5 5.5 5 5 N load 55 4.5 4.5 4 4 3.5 3.5 N load 55 3 3 2.5 2.5 background nitrate=3.01 mg/L 2 2 Nitrate concentration (mg/L) Nitrate concentration (mg/L) 1.5 1.5 1 1 0.5 0.5 background nitrate=0.73 mg/L 0 0 0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 Number of septic tanks Number of septic tanks Figure 15f. Projected septic-tank density versus nitrate concentration for domain 6 (table 4) in Cache Valley, Cache Figure 15e. Projected septic-tank density versus nitrate concentration Figure 15f. Projected septic-tank density versus nitrate concentration for domain 5 (table 4) in Cache Valley, Cache County, Utah, based on for domain 6 (table 4) in Cache Valley, Cache County, Utah, based on 500 existing septic tanks (see table 5). N load 55 refers to an estimat- 190 existing septic tanks (see table 5). N load 55 refers to an estimated nitrate loading per liter of wastewater from septic-tank systems (see ed nitrate loading per liter of wastewater from septic-tank systems (see text for explanation). text for explanation). 24 Utah Geological Survey

Septic tank density (acres/system) Septic tank density (acres/system) 59 3 144 3.9 6 4 5.5 3.5 5 4.5 3

4 N load 55 2.5 3.5 N load 55 3 2 2.5 1.5 2 Nitrate concentration (mg/L) 1.5 Nitrate concentration (mg/L) 1 1 0.5 0.5 background nitrate=0.09 mg/L background nitrate=0.3 mg/L 0 0 0 500 1000 1500 2000 2500 3000 3500 4000 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 Number of septic tanks Number of septic tanks Figure 15g. Projected septic-tank density versus nitrate concentration Figure 15h. Projected septic-tank density versus nitrate concentration for domain 7 (table 4) in Cache Valley, Cache County, Utah, based on for domain 8 (table 4) in Cache Valley, Cache County, Utah, based on 200 existing septic tanks (see table 5). N load 55 refers to an estimat- 100 existing septic tanks (see table 5). N load 55 refers to an estimated nitrate loading per liter of wastewater from septic-tank systems (see ed nitrate loading per liter of wastewater from septic-tank systems (see text for explanation). text for explanation).

Septic tank density (acres/system) Septic tank density (acres/system) 49 1.8 49 3.5 5 5

4.5 4.5

4 4

3.5 3.5 N load 55 N load 55 3 3

2.5 2.5

2 2 1.5

1.5 Nitrate concentration (mg/L) Nitrate concentration (mg/L) 1 1

background nitrate=0.92 mg/L 0.5 0.5 background nitrate=0.35 mg/L 0 0 0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 0 2500 5000 7500 10000 12500 15000 17500 20000 22500 Number of septic tanks Number of septic tanks Figure 15i. Projected septic-tank density versus nitrate concentration Figure 15j. Projected septic-tank density versus nitrate concentration for domain 9 (table 4) in Cache Valley, Cache County, Utah, based on for domain 10 (table 4) in Cache Valley, Cache County, Utah, based on 250 existing septic tanks (see table 5). N load 55 refers to an estimat- 800 existing septic tanks (see table 5). N load 55 refers to an estimated nitrate loading per liter of wastewater from septic-tank systems (see ed nitrate loading per liter of wastewater from septic-tank systems (see text for explanation). text for explanation).

Septic tank density (acres/system) Septic tank density (acres/system) 106 1.9 26 1.8 11 6 10.5 5.5 10 9.5 5 N load 55 9 4.5 8.5 8 4 N load 55 7.5 3.5 7 6.5 3 6 background nitrate=6.58 mg/L 2.5 5.5 5 2 Nitrate concentration (mg/L) Nitrate concentration (mg/L) 4.5 1.5 4 3.5 1 3 0.5 background=0.63 mg/L 2.5 2 0 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 Number of septic tanks Number of septic tanks Figure 15k. Projected septic-tank density versus nitrate concentration Figure 15l. Projected septic-tank density versus nitrate concentration for domain 11 (table 4) in Cache Valley, Cache County, Utah, based on for domain 12 (table 4) in Cache Valley, Cache County, Utah, based on 100 existing septic tanks (see table 5). N load 55 refers to an estimat- 400 existing septic tanks (see table 5). N load 55 refers to an estimated nitrate loading per liter of wastewater from septic-tank systems (see ed nitrate loading per liter of wastewater from septic-tank systems (see text for explanation). text for explanation). Special Study 101 25 o o 11200 11145' o R. 2 W. R.1 E. T. 3 E.

11130' o S# S# 42 00'

S# Lewiston 1 33 41o 57' 30" 2 S# S# S# Cove Clarkston S# S# T.14 N. S# T.14 N. 4 B e ar S# S#S# S# S# S# S# S# Richmond Newton Trenton River k S# ee Cr 5 S# t S# mmi Su Amalga S# S#S# S# S# C S# S# S# u Smithfield tl er S# S# S# S# S# S# S# S# S# S# S# R S# 6 S# S# e S# S# s S# e S# S# S# Hyde Park rv S# 7 S# o S# S# S# S# i r S# BEAR S# S# S# S# S# r ive 8 S# R S# S# S# n o ga 41 45' S#S# Logan Lo o S# S# 41 45' #S# S# S RIVER S# S# S# S# 9 S# S# S# S# S# S# S# S# Mendon S# S# S# S# Providence S# S# S# # S# S# S S# S# S# # S# S# # S S# S# S#S S# RANGE S# Li S# ttl S# S# e S# S# S# S# S# 10 Nibley T.11 N. S# S# S# T.11 N. S# # S# S S# S# S# S#S# S# S# S# S# S# S# WellsvilleS# S# S# B Hyrum e Fork ar B S# lacksmith S# S# S# S# S# S# S# S# S# S# S# S# S# S# S# S# S# S#

R 12

11 v e S#S# Explanation r S# Paradise o S# Sampled Wells S# 11200' S# 7 Domain number S# S#S# S#Avon One-third system maximum per acre T.9 N. T.9 N. (3 acres/system) 41 o 30' 41 o 30' One-fifth system maximum per acre (5 acres/system)

One-tenth system maximum per acre (10 acres/system)

40-acre minimum (FR-40) o

Sewered communities/area R.3E. 11130'

R.1E.

Flow-area boundary (domain boundary) N

Municipal boundaries o

411145' Road

Water course 5 0 5 Miles Water bodies 505Kilometers Study area

Figure 16. Recommended lot size for ground-water flow domains in Cache Valley, Cache County, Utah. 26 Utah Geological Survey septic-system density of about 0.12 systems per acre (0.05 tank systems is likely to be greatest. We performed a simple systems/hm2), or 8.4 acres per system (3.4 hm2/system) in mass-balance evaluation of the shallow unconfined aquifer to domain 4 (table 6). help understand the effect of increasing numbers of septic tanks on water quality in the shallow unconfined aquifer; Shallow Unconfined Ground-Water Issues once again, we used nitrate as a proxy for all constituents in septic-tank system effluent. However, we note that negligi- We have applied the mass-balance approach to the prin- ble data exist for the shallow unconfined aquifer compared to cipal drinking-water aquifer in the basin fill of Cache Valley, the principal aquifer. because this is the resource we believe warrants the greatest The general physical characteristics of the shallow efforts for protection. Some regulatory agencies may be con- unconfined aquifer are summarized in table 7. The thickness cerned about the impact of septic tanks on all waters of the of the shallow unconfined aquifer as reported in Bjorklund state, including shallow unconfined ground water in Cache and McGreevy (1971) was 10 to 20 feet (3-6 m), but the Valley that is not currently used as a source of drinking water aquifer thickness is probably not continuous across the val- and, in much of the valley, is separated from the principal ley. We used 20 feet (6 m) as the thickness of the unconfined aquifer by thick clay confining layers. In many areas of aquifer. We considered the unconfined aquifer to consist of Cache Valley there is also an upward ground-water gradient fine sand, silt, and clay, and we used a hydraulic conductivi- in the principal aquifer (discharge area, figure 6) that can pre- ty of 0.5 feet per day (0.15 m/d), a value typical for these vent downward migration of poorer quality water in the shal- types of sediment (Freeze and Cherry, 1979). We obtained low unconfined aquifer. the hydraulic gradient from the potentiometric surface map The shallow unconfined aquifer in Cache Valley was not in Bjorklund and McGreevy (1971) for the unconsolidat- a component of the Kariya and others (1994) ground-water basin-fill deposits, and assumed this hydraulic gradient ap- flow model of the unconsolidated aquifer in Cache Valley. plied to the shallow aquifer; we used an average hydraulic Because the shallow unconfined aquifer is relatively thin and gradient for the valley of 0.01 in our calculations. Using an is in proximity to surface sources of ground-water pollution, average valley width of 7 miles (11 km), we obtained a vol- the shallow unconfined aquifer is where the impact of septic- umetric flow rate of 3,696 cubic feet per day (105 m3/d) for

Table 6. Results of mass-balance analysis using an estimated nitrogen loading of 55 mg/L for each ground-water flow domain in Cache Valley, Cache County, Utah.

Domain Total # Septic Current Calculated* Recommended projected systems density density density septic beyond acres/ septic acres/ septic acres/ septic systems current septic system septic system septic system number system /acre system /acre system /acre

1 1,525 1,425 91 0.011 6 0.17 10 0.1

2 2,675 2,375 67 0.015 7.5 0.13 10 0.1

3 1,900 1,790 57 0.018 3.2 0.31 5 0.2

4 3,450 2,920 55 0.018 8.4 0.12 10 0.1

5 6,550 6,050 50 0.02 3.8 0.26 5 0.2

6 2,700 2,510 112 0.009 7.9 0.13 10 0.1

7 3,900 3,700 59 0.017 3.0 0.33 3 0.3

8 3,675 3,575 144 0.007 3.9 0.26 5 0.2

9 3,425 3,175 49 0.02 3.5 0.28 5 0.2

10 22,000 21,200 49 0.02 1.8 0.56 3 0.3

11 5,600 5,500 106 0.009 1.9 0.53 3 0.3

12 5,700 5,300 26 0.039 1.8 0.56 3 0.3

* best-estimate calculation is based on a nitrogen load of 17 g N per capita per day (from Kaplan, 1988) for a 3.24-person household and 227 gallons of wastewater per day for the Bear River Basin (Utah Division of Water Resources, 2001). Special Study 101 27

parameters described above. Due to the greater amount of Table 7. Physical characteristics of the unconfined aquifer in ground-water available for mixing in the central areas of Cache Valley, Cache County, Utah. Cache Valley, a greater number of septic systems can exist in those areas compared to the northeastern area of Cache Val- Thickness 20 feet ley, especially near Lewiston and Cove. However, the results of this study would be most effective in protecting ground- Hydraulic conductivity 0.5 feet per day water quality through land-use planning when used in conjunction with ground-water quality classification and Hydraulic gradient 0.01 ground-water recharge/discharge-area maps. Additionally, switching from septic-tank systems to a well-engineered, Average width 7 miles well-constructed public sanitary sewer system, especially one that includes tertiary treatment capabilities, would be a Background nitrate 0.68 mg/L preferred alternative where protection of ground-water quality is a primary issue; however, poorly engineered, poorly constructed public sanitary sewer systems could have even greater negative impacts on ground-water quality than septic- the Utah part of Cache Valley. The Utah part of Cache Val- 2 tank systems. ley was assumed to be about 365 square miles (945 km ). The ground-water flow generated domain boundaries on For our calculations we used a density of about 0.01 septic- plate 9 do not coincide with geographic or cultural features tank systems per acre (0.004 systems/hm2), or 100 acres per 2 that can be easily located on the land surface for application system (40 hm /system). We had no representative chemical in land-use planning. Plate 10 shows the results of our sep- data on the shallow unconfined aquifer, so we used the val- tic-tank-system/water-quality degradation analysis with the ley-wide average of 0.68 mg/L for the background nitrate domain boundaries shifted slightly to match geographic or loading for our calculations. cultural features; this facilitates application of our analysis in The effect of septic-tank systems on ground-water qual- land-use planning. These maps are designed to be land-use- ity in the shallow unconfined aquifer is considerable. An planning tools, especially in areas where public sanitary additional 0.4 percent, or 10 septic tanks, increases the sewer systems are not available, not as an alternative to sew- nitrate concentration from the background value of 0.68 ering; we believe development of public sanitary sewer sys- mg/L to 4.8 mg/L, an increase of seven times. Similarly, an tems should continue to be implemented where feasible. In additional 3 percent, or 100 septic tanks, increases the nitrate addition, these maps are not suitable for subdivision-scale concentration from the background value of 0.68 mg/L to 25 planning. In the future, if regulatory agencies determine that mg/L, a 36-fold increase. The accumulation of nitrate in the the shallow unconfined aquifer should be protected from shallow unconfined aquifer is a cumulative effect of septic- degradation from septic-tank systems, either (1) additional tank disposal practices. The addition of the septic-tank efflu- data collection followed by construction of a ground-water ent to the shallow unconfined aquifer is a substantial propor- flow model for the shallow unconfined aquifer system should tion of the volume of recharge water to the aquifer. Because be undertaken to allow further analyses of septic-tank system water quality in the shallow unconfined aquifer is impacted density/water-quality degradation, or (2) public sanitary- by the quality of this recharge water, the implication of the sewer-system development should be considered throughout nitrate loading with respect to the impact of septic-tank sys- Cache Valley. tems on ground water is that the shallow unconfined aquifer is probably already overloaded in some areas due to the number of septic-tank systems already in place. If the shallow ground-water system is determined by regulatory agencies to SUMMARY AND CONCLUSIONS be a resource that should be protected from degradation from septic-tank systems, our mass-balance analysis indicates that Ground water is the most important source of drinking no new septic-tank systems should be added to the ground- water in Cache Valley. Ground-water quality classification is water system, and removal of existing systems, where feasi- a relatively new tool that can be used in Utah to manage ble, would be beneficial to water quality in the shallow potential ground-water contamination sources and protect unconfined aquifer. However, because of the general lack of the quality of ground-water resources. The results of the data regarding the shallow unconfined aquifer, data collec- ground-water quality classification for Cache Valley, which tion followed by construction of a ground-water flow model was formally adopted by the Utah Water Quality Board on for the unconfined aquifer system may be warranted so that August 10, 2001, indicate that the basin-fill aquifer contains further analyses of septic-system density/water-quality de- mostly high-quality ground-water resources that warrant pro- gradation may be conducted. tection. Eighty-four percent of the ground water in the basin- fill aquifer is classified as Class IA, and 16 percent is classi- Recommendations for Land-Use Planning fied as Class II, based on chemical analyses of water from 163 wells sampled during fall 1997 and winter/spring 1998 Our estimates of nitrate concentrations/water-quality (TDS range of 178 to 1,750 mg/L). degradation provide a conservative (worst case) first approx- Septic tank soil-absorption systems are used to dispose imation of long-term ground-water pollution from septic- of domestic wastewater in many areas of Cache Valley. tank systems. The graphs of projected nitrate concentration Many constituents in septic-tank effluent are known to versus number of septic-tank systems in each area show rec- undergo little remediation in the soil environment as they ommended septic-tank density for each domain based on the travel through the unsaturated zone to the aquifer; dilution is 28 Utah Geological Survey the principal mechanism for lowering concentrations of these ACKNOWLEDGMENTS constituents once they have reached the aquifer. We used nitrate in septic-tank effluent as an indicator constituent for The Cache Valley ground-water quality classification evaluating the dilution of constituents in wastewater that project was funded by a U.S. Environmental Protection Ag- reach ground-water aquifers; this evaluation uses a mass-bal- ency Nonpoint Source Program grant through the Utah Divi- ance approach that is based principally on ground-water flow sion of Water Quality. The Utah Division of Water Quality available for mixing with effluent constituents in the aquifer contributed water-quality sampling and analysis for this of concern. The mass-balance approach for the principal report; water-well owners were cooperative in permitting the basin-fill aquifer in Cache Valley, Utah, indicates that three sampling of their wells. Mike Robinson, Utah State Univer- categories of recommended maximum septic-tank system sity graduate student, arranged for guides to help Utah Divi- densities are appropriate for development using septic tank sion of Water Quality sampling crews locate some of the soil-absorption systems for wastewater disposal in Cache wells we selected for sampling in Cache Valley. The septic- Valley, Utah: one-third, one-fifth, and one-tenth systems per tank-density/water-quality degradation analysis was funded acre (0.13, 0.08, and 0.04 systems/hm2), or 3, 5, and 10 acres by Cache County. We thank Nick Galloway, Bear River Dis- per system (1.2, 2, and 4 hm2/system); these recommenda- trict Health Department, for supplying estimates for the num- tions are based on hydrogeologic parameters incorporated in ber of septic-tank systems in each of our ground-water flow the ground-water flow model and geographically divided domains, and Mark Teusher, Cache County Planner, for sup- into 12 ground-water flow domains on the basis of flow-vol- plying GIS files to be used for our project. Thad Erickson, ume similarities. The shallow unconfined aquifer is a limit- Cache County Water Policy Coordinator, was instrumental in ed source of drinking water in Cache Valley, Utah; however, helping us get the funding for both the ground-water quality our mass-balance analyses indicate that this aquifer is vul- classification and septic-tank-density/water-quality degrada- nerable to degradation from development using septic sys- tion projects. We thank Chris Eisinger, Basia Matyjasik, tems for wastewater disposal. If regulatory agencies desire Kim Nay, Alison Corey, and Matt Butler, Utah Geological to protect this shallow unconfined aquifer from water-quali- Survey, for preparing the figures for this report. We thank ty degradation, we recommend that either (1) additional data Bill Damery and John Whitehead, Utah Division of Water collection followed by construction of a ground-water flow Quality; Robert Q. Oaks, Jr., Department of Geology, Utah model for the shallow unconfined aquifer system be under- State University; Hugh Hurlow, Mike Hylland, and Kimm taken to allow further analyses of septic-tank system densi- Harty, Utah Geological Survey; and Larry Spangler, Jim ty/water-quality degradation, or (2) no new septic-tank sys- Mason, and Connie Allen, U.S. Geological Survey; for their tems be considered in Cache Valley, Utah. reviews and helpful comments. Special Study 101 29

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Williams, J.S., 1948, Geology of the Paleozoic rocks, Logan U.S. Environmental Protection Agency, 2002, Current drinking quadrangle, Utah: Geological Society of America Bulletin, water standards: Online, http://www.epa.gov/safewater/ v. 59, p. 1121-1164. mcl.html, accessed November 18, 2002. —1958, Geologic atlas of Utah, Cache County: Utah Geologi- Utah Division of Water Quality, 1998, Aquifer classification cal and Mineral Survey Bulletin 64, p. 1-103 guidance document: Salt Lake City, unpublished Utah Divi- —1962, Lake Bonneville – geology of southern Cache Valley, sion of Water Quality report, 9 p. Utah: U.S. Geological Survey Professional Paper 257-C, p. Utah Division of Water Resources, 1992, Utah state water plan, 131-152. Bear River basin: Salt Lake City, Utah Department of Nat- —1964, The age of the Salt Lake Group in Cache Valley, Utah- ural Resources, variously paginated. Idaho: Utah Academy of Sciences, Arts, and Letters Pro- —2001a, Utah’s water resources – planning for the future: Salt ceedings, v. 41, part II, p. 269-277. Lake City, Utah Department of Natural Resources, 72 p. Zhan, Honbin, and McKay, W.A., 1998, An assessment of nit- —2001b, Municipal and industrial water supply and uses in the rate occurrence and transport in Washoe Valley, Nevada: Bear River Basin: Salt Lake City, Utah Department of Nat- Environmental and Engineering Geoscience, v. 4, no. 4, p. ural Resources, 113 p. 479-489. APPENDIX A.1. EPA primary ground-water quality standards and analytical method for some chemical constituents sampled in Cache Valley, Cache County, Utah. EPA GROUND-WATER CHEMICAL CONSTITUENT ANALYTICAL QUALITY METHOD STANDARD (mg/L) Nutrients: total nitrate/nitrite 353.2 10.0 ammonia as nitrogen 350.3 - total phosphorous and dissolved total phosphate 365.1 - Dissolved metals: arsenic 200.9 0.05 barium 200.7 2.0 cadmium 200.9 0.005 chromium 200.9 0.1 copper 200.7 1.3 lead 200.9 0.015 mercury 245.1 0.002 selenium 200.9 0.05 silver 200.9 0.1 zinc 200.7 5.0

General Chemistry: total dissolved solids 160.1 2000+** or (500*++) pH 150.1 between 6.5 and 8.5 aluminum* 200.7 0.05 to 0.2 calcium* 200.7 - sodium* 200.7 - bicarbonate 406C - carbon dioxide 406C - APPENDIX A.1. (continued).

EPA GROUND-WATER CHEMICAL CONSTITUENT ANALYTICAL QUALITY METHOD STANDARD (mg/L) carbonate 406C - chloride* 407A 250 total alkalinity 310.1 - total hardness 314A - specific conductance 120.1 - iron* 200.7 0.3 potassium* 200.7 - hydroxide 406C - sulfate *++ 375.2 250 magnesium* 200.7 - manganese* 200.7 0.5 Organics and pesticides: aldicarb 531.1 0.003 aldicarb sulfoxide 531.1 0.004 atrazine 525.2 0.003 carbofuran 531.1 0.04 2, 4-D 515.1 0.07 methoxychlor 525.2 0.4 methiocarb 531.1 - dinoseb 515.1 0.007 dalapon 515.1 0.2 baygon 515.1 - picloram 515.1 0.5 dicamba 515.1 - APPENDIX A.1. (continued).

oxamyl 531.1 0.2 methomyl 531.1 - EPA GROUND-WATER CHEMICAL CONSTITUENT ANALYTICAL QUALITY METHOD STANDARD (mg/L) carbaryl 531.1 - 3-Hydroxycarbofuran 531.1 - pentachlorophenol 515.1 0.001 2, 4, 5-TP 515.1 0.05 Radionuclides: Alpha, gross 600/4-80-032 15 pCi/L(picocuries per liter) Beta, gross 600/4-80-032 4 millirems per year U238MS Fil (Uranium) 600/4-80-032 0.030 mg/L 226Radium 600/4-80-032 5 pCi/L 228Radium 600/4-80-032 5 pCi/L

- no standard exists for this constituent *for secondary standards only (exceeding these concentrations does not pose a health threat) + maximum contaminant level is reported from Utah Administrative Code R309-103 (Utah Division of Water Quality) **For public water-supply wells, if TDS is greater than 1,000 mg/L, the supplier shall satisfactorily demonstrate to the Utah Water Quality Board that no better water is available. The Board shall not allow the use of an inferior source of water if a better source of water (lower in TDS) is available ++TDS and sulfate levels are given in the Primary Drinking Water Standards, R309-103- 2.1. They are listed as secondary standards because levels in excess of these recommended levels will likely cause consumer complaint APPENDIX A.2. Water-quality data Total Well Field Fe, Chlor- Alpha, Beta, 226 Hardness/ Sample Depth NO2+NO3 TDS T Arsenic Dissolved ide SO4 Na gross gross Radium CaCO3 Site # date USGS Cadastral (feet) (mg/L) (mg/L) ((C) pH (g/L) (g /L) (mg/L) (mg/L) (mg/L) (pCi/L) (pCi/L) (pCi/L) (mg/L) 1 12-10-97 (B-14-2) 34aac 70 <.02 528 10 7.1 19 403 30.5 66 18.8 - - - 284.1 1.5 12-10-97 (B-14-2) 26cdb 35 1.31 238 6 7.3 <5 <20 8.5 <10 7.46 - - - 227.3 2 10-15-97 (B-14-2) 26cda 32 8.78 540 11.9 7.2 12 <20 33 31.2 31 - - - 437.2 2.5 12-10-97 (B-14-2) 35bbb 80 32.85 708 9.6 7 12 <20 49 49 31.8 - - - 417.1 " " - 35.77 ------3 10-15-97 (B-14-2) 26ddb 90 15.72 674 10.5 7.3 15 65.5 86 98.8 40.2 4.14 <10 1.09 484.9 " - " - 8.67 ------" - " - 6.51 ------5 10-15-97 (B-14-1) 5add 110 0.03 534 15.4 7.8 27 1010 96 80.5 92.9 - - - 245.2 7 12-10-97 (B-14-1) 28bdd 70 1.57 244 5.9 7.7 <5 <20 8.5 <10 7.75 - - - 237.3 555 5-13-97 (A-15-1) 31cdc - 12.17 1758 9.5 7.5 - - 360 305 326 - - - 737.6 556 5-13-97 (A-15-1) 31dcc - 9.25 1468 9.7 7.9 - - 312.5 269 265 - - - 643.8 14 10-15-97 (A-14-1) 15abb 40 6.02 306 13.2 7.4 <5 <20 15 <10 10.2 - - - 293.2 14.5 12-09-97 (A-14-1) 15cdc 175 1.6 226 9.7 7.6 <5 <20 7 <10 12.2 - - - 181.4 15 12-16-97 (A-14-1) 22bad 59 3.93 282 10.1 7.8 <5 <20 8 <10 6.21 - - - 262.4 16 10-15-97 (A-14-1) 10dcc 83 <.02 296 13.5 7.7 25 998 63 <10 42.9 - - - 202.1 17 12-09-97 (A-14-1) 34adb 52 0.28 370 10.6 7.1 <5 <20 11.7 <10 13.8 - - - 244.1 20 12-09-97 (A-14-1) 14caa 220 3.13 232 8.6 7.4 <5 <20 7 <10 10.5 - - - 204.6 20.5 12-09-97 (A-13-1) 11bbb-1 21 1.73 290 6.8 7.7 <5 <20 13 <10 14.8 - - - 214.5 501 5-13-98 (A-14-1) 16ddd 180 0.19 286 10.1 7.9 - - 31.5 <10 33.5 - - - 208.6 502 5-13-98 (A-14-1) 16dda 260 0.26 302 10.9 7.9 39 834 50.5 <10 53.6 - - - 177.5 504 5-13-98 (A-14-1) 34bdd 7.74 394 10.6 7.6 - - 16 <10 9.71 - - - 353.9 22 12-10-97 (B-13-1) 30cba 109 2.82 366 11.8 7.6 16 <20 57 22 86.2 - - - 118.3 25 12-10-97 (B-13-1) 22cbc 436 <.02 860 7.4 7.8 <5 1280 75 <10 137 - - - 427.3 26 12-10-97 (B-13-1) 27bcc 50 0.04 728 9.5 7 <5 2770 250 <10 138 7.68 17.3 <.5 302.9 26.5 12-11-97 (B-12-1) 1cbc 595 0.23 974 16.4 7.5 <5 307 490 <10 97.3 - - - 534.5 27 12-11-97 (A-13-1) 31ccc 626 0.16 590 15.5 7.2 46 1210 156 <10 141 - - - 232.7 27.5 12-11-97 (A-12-1) 2add 575 <.02 964 9.8 8 <5 228 485 <10 97.9 - - - 581.1 28.5 12-16-97 (B-12-1) 11bad 616 0.23 696 18 7.5 <5 243 242.5 <10 89 - - - 317.2 29 12-11-97 (B-12-1) 11ccd 947 0.03 564 20.2 7.7 <5 646 232.5 <10 75 - - - 323.1 30 12-11-97 (B-13-1) 35ccd 600 <.02 1010 16.5 7.5 <5 332 515 <10 94.5 - - - 532.8 31 12-11-97 (B-13-1) 35daa 640 0.64 866 15 7.7 <5 1970 435 <10 96.8 - - - 496.4 31.5 12-11-97 (B-13-1) 35aaa 2.34 260 5.8 7.9 <5 <20 8 <10 9.26 5.98 <10 <.5 203 32 12-10-97 (B-13-1) 27bda 918 <.02 712 19.6 7.1 <5 575 285 <10 107 - - - 351.7 33 12-16-97 (B-12-1) 13bcb 568 0.81 230 7.4 8 <5 21.8 10 <10 21.8 - - - 123.3 34 12-11-97 (B-13-1) 36cca 723 <.02 994 13.9 7.5 <5 3030 500 <10 94.8 - - - 545.3 35 12-16-97 (B-13-1) 31acc 90 4.51 456 9.1 7.8 13 <20 68.5 35 71.3 - - - 213.3 36 12-16-97 (B-12-1) 12acc 504 <.02 886 12.4 7.6 13 1010 405 <10 85.1 - - - 468 37 12-11-97 (A-12-1) 6cbc 514 <.02 488 11.6 7.7 <5 196 107.5 <10 68 - - - 268.5 38 12-11-97 (A-12-1) 6cbb 535 <.02 536 14.1 7.8 <5 <20 227.5 <10 60.2 - - - 334.5 40 12-11-97 (B-12-1) 24dad 310 <.02 258 10.4 7.6 5.4 466 17.5 <10 31.5 - - - 177.1 41.5 12-10-97 (A-13-1) 29adc 100 3.79 290 10.5 7.1 <5 <20 9.5 <10 8.77 - - - 207.8 42 12-02-97 (A-12-1) 8aab 142 <.02 312 12.5 7.7 12 351 40.5 <10 61 - - - 168.7 43 12-10-97 (A-12-1) 5ada 75 0.98 334 10.3 7.3 <5 1760 16 <10 24.8 - - - 192.1 44 12-03-97 (A-12-1) 17daa-2 19.6 2.55 280 17.7 7.5 <5 <20 7.5 <10 19.1 - - - 178.4 44.5 12-09-97 (A-13-1) 34dab 175 0.39 318 9.8 7.6 <5 23.5 12 <10 6.77 - - - 297 45 12-03-97 (A-12-1) 20add 145 3.43 318 16.6 7.4 <5 <20 15.5 11 23.1 5.23 <10 <.5 205.9 45.5 12-03-97 (A-12-1) 9bbd 67 <.02 336 10.3 7.7 100 (120) 992 27 <10 80.9 - - - 135.2 46 12-10-97 (A-13-1) 33bbb 147 3.09 290 12.1 7.2 <5 <20 6.5 <10 14.1 - - - 188.6 46.5 12-09-97 (A-12 -1) 10cdc 190 <.02 344 11.6 7.8 <5 467 10 <10 44.9 - - - 239 47 12-16-97 (A-12-1) 9ccb 235 1.38 282 13.6 7.8 <5 <20 11.7 12 34.8 - - - 188 47.5 12-09-97 (A-12-1) 14baa 152 2.33 312 7.8 7.6 7.7 <20 11 <10 11.3 - - - 285.4 48.5 12-03-97 (A-12-1) 20caa-1 118 2.08 268 18 7.5 <5 <20 13 <10 20.6 - - - 213.5 49 12-10-97 (A-13-1) 29bba 257 4.12 308 9.6 7 <5 57 12 <10 9.33 - - - 206 Total Well Field Fe, Chlor- Alpha, Beta, 226 Hardness/ Sample Depth NO2+NO3 TDS T Arsenic Dissolved ide SO4 Na gross gross Radium CaCO3 Site # date USGS Cadastral (feet) (mg/L) (mg/L) ((C) pH (g/L) (µg/L) (mg/L) (mg/L) (mg/L) (pCi/L) (pCi/L) (pCi/L) (mg/L) 50 12-03-97 (A-12-1) 16dbc 67 2.64 302 17.4 7.4 <5 <20 7 <10 12.9 - - - 272.4 51 12-16-97 (A-13-1) 15bad 166 0.11 308 6.4 7.9 17 <20 17.5 31 14.2 - - - 0.045 51.5 12-03-97 (A-12-1) 30aaa 161 0.23 262 15.1 7.6 5.6 571 9 <10 22.8 - - - 214.4 52 12-10-97 (A-13-1) 16abb 154 5.2 504 10.3 7 <5 <20 13 13 26.2 - - - 415.6 53 12-03-97 (A-12-1) 10bcc 106 4.38 314 13.5 7.5 <5 <20 10 <10 16.6 - - - 266.7 54 12-03-97 (A-12-1) 15cbc 177 2.37 308 15.6 7.3 <5 <20 6.5 <10 12.1 - - - 250.2 55 12-10-97 (A-13-1) 20add 125 0.78 264 8.2 7.2 <5 <20 5.5 <10 8.72 - - - 251 55.5 12-09-97 (A-12-1) 15aca 60 2.29 278 11.1 8.1 <5 <20 15.5 24 47.8 - - - 151 56 12-09-97 (A-12-1) 3cac 135 7.08 354 9 7.4 <5 <20 15.5 <10 11.2 - - - 325.7 57 12-09-97 (A-12-1) 13dba 94 2.63 360 10.3 7.4 <5 22 5.5 <10 13.2 - - - 333 58 12-10-97 (A-13-1) 21cbb 140 2.68 234 10.4 7.2 <5 <20 5 <10 8.08 - - - 195.6 59 12-03-97 (A-12-1) 28cbb 0.86 248 17.5 7.6 <5 <20 10.5 15 12.9 - - - <.01 60 12-16-97 (A-12-1) 11dcb 205 2.03 266 9.4 7.7 <5 <20 4 <10 4.33 5.19 <10 <.5 265.3 61 12-03-97 (A-12-1) 28bcc 74 <.02 302 15.2 7.5 <5 111 24 20 33.8 - - - 205 61.5 12-10-97 (A-13-1) 28bba 85 2.85 270 7.9 7.1 <5 <20 10 <10 6.21 - - - 269.1 889 5-13-98 (A-12-1) 9bac 0.26 346 10.8 8.2 - - 35.5 <10 83.9 - - - 123.9 63 12-02-97 (B-12-1) 32cda 63 7.56 664 9 7.2 5.7 <20 108 11 36.6 - - - 408.7 63.5 11-20-97 (B-11-1) 24cdb 145 0.27 348 10.4 7.6 <5 <20 7 92 6.55 - - - 305 64.5 11-20-97 (B-11-1) 27bbb 400 1.66 352 10 7.6 <5 94.5 43.5 <10 56.2 - - - 194.4 65 12-02-97 (B-12-1) 29cda 200 0.02 358 11.8 8.3 <5 287 8.5 <10 112 - - - 34.7 65.5 12-02-97 (B-11-1) 27aab 100 <.02 334 9.8 7.5 <5 1420 55 <10 45.1 - - - 206.1 66 12-02-97 (B-11-1) 16cdb 121 1.52 334 10.6 7.5 <5 <20 7.5 <10 50.5 3.99 <10 - 196.3 66.5 12-02-97 (B-11-1) 34bda 160 0.67 262 9.2 7.6 <5 31.9 40.5 <10 21.9 - - - 207.8 67 12-02-97 (B-11-1) 16acb-1 82 <.02 354 8.7 7.4 14 1020 37.5 <10 57.8 - - - 188.7 67.5 11-20-97 (B-11-1) 35bcb 40 1.46 304 10.4 7.5 <5 <20 39 <10 22.2 - - - 247.7 68 11-20-97 (B-11-1) 1ccc 206 0.03 320 10.2 7.8 <5 1920 35.5 <10 32.3 - - - 187.8 68.5 12-03-97 (B-11-1) 35aba 195 <.02 364 8.6 7.5 19 1100 19.5 <10 21.8 - - - 251.7 69 12-02-97 (B-11-1) 27cbd 126 1.22 258 9.5 7.8 <5 94.2 8.5 <10 20.6 - - - 210.1 69.5 11-20-97 (A-11-1) 6abd 183 0.43 244 12.4 7.8 <5 <20 15.5 <10 15.6 - - - 202.3 70 11-20-97 (B-11-1) 14cba 238 <.02 330 10.8 7.5 11 585 12 48 15.7 - - - 271.9 70.5 11-20-97 (A-11-1) 7bdd 125 1.46 286 10.9 7.6 <5 <20 8 22 8.05 - - - 260.9 71.5 12-02-97 (B-11-1) 36abb 245 <.02 352 10.1 7.4 26 1030 14 <10 19.4 - - - 314.3 72 11-20-97 (B-11-1) 2cad 420 <.02 432 11 7.7 <5 726 117.5 <10 49.2 - - - 259.8 72.5 11-20-97 (B-10-1) 2aca <.02 350 7.4 7.4 <5 1840 38.5 <10 30.1 - - - 240.1 73 12-02-97 (B-11-1) 2cca 238 <.02 326 9.4 7.5 <5 574 22.5 <10 24.9 - - - 197.5 73.5 11-20-97 (B-11-1) 1ccc 155 0.05 324 10.7 7.7 <5 1530 40 16 32.6 - - - 250.1 74 11-20-97 (B-11-1) 35acc-3 84 <.02 376 9.5 7.5 6.3 1490 36.5 <10 30.1 - - - 280.9 75 11-20-97 (B-11-1) 11dcd 230 <.02 324 11.2 7.6 <5 347 7.5 70 9.34 - - - 288.8 76 11-20-97 (B-11-1) 11daa 190 <.02 336 11.5 7.7 <5 349 46 27 33.6 - - - 242.6 77 11-20-97 (B-11-1) 13dbc 100 0.56 314 11 7.6 <5 <20 15.5 57 10.4 - - - 264.2 78 12-02-97 (B-11-1) 25bbc 150 <.02 350 10.9 7.4 22 642 10.2 68 12.5 - - - 304.4 79 11-20-97 (B-11-1) 13aab 81 0.47 324 11.6 7.6 <5 <20 13 46 15.4 - - - 245.1 80 12-02-97 (B-12-1) 36caa 263 0.25 258 12.4 7.8 <5 <20 28.5 <10 17.4 - - - 222 81 12-02-97 (B-11-1) 16bbc 140 <.02 270 10 7.5 11 7560 20 <10 32.6 - - - 174.8 82 12-02-97 (B-11-1) 36dcc 180 <.02 366 10 7.3 <5 261 15.5 11 14 - - - 297.4 83 12-02-97 (A-11-1) 31dbc 137 4.09 254 - - <5 <20 5 <10 4.22 - - - 253.9 84 12-02-97 (B-11-1) 25aca 200 0.29 340 10.2 7.5 <5 <20 14.5 90 6.28 12.1 10.2 <.5 307.5 85 11-20-97 (B-11-1) 1dab 178 <.02 324 10.4 7.6 <5 1100 35.5 <10 36.5 <2 <10 <.5 182.5 86 11-20-97 (B-11-1) 24add 130 0.46 298 10.1 7.6 <5 <20 6 61 5.6 - - - 256.7 87 11-20-97 (B-11-1) 21bac 129 4.21 312 10.4 7.5 <5 <20 10 <10 19.1 - - - 250.2 87.5 12-02-97 (B-11-1) 21bdd 140 2.85 250 11.2 7.4 <5 <20 10.2 <10 10.7 - - - 214.7 88 12-02-97 (A-12-1) 31bcd 176 2.54 248 11.7 7.9 <5 <20 9.5 <10 14.2 - - - 214.5 412 12-16-97 (A-11-1) 19bbc 100 0.75 334 9.8 7.8 <5 <20 10.5 62 8.25 - - - 292.3 413 12-16-97 (A-11-1) 30bbb 213 0.18 328 11.8 7.6 <5 <20 6.5 69 8.15 - - - 258 414 12-16-97 (A-11-1) 31ccd 159 <.02 492 11.6 7.5 <5 4830 38.5 31 37.1 - - - 347.1 Total Well Field Fe, Chlor- Alpha, Beta, 226 Hardness/ Sample Depth NO2+NO3 TDS T Arsenic Dissolved ide SO4 Na gross gross Radium CaCO3 Site # date USGS Cadastral (feet) (mg/L) (mg/L) ((C) pH (g/L) (µg/L) (mg/L) (mg/L) (mg/L) (pCi/L) (pCi/L) (pCi/L) (mg/L) 415 12-03-97 (A-11-1) 30bcb 201 0.61 314 12.3 7.7 <5 <20 8.5 73 6.18 - - - 288.9 416 12-02-97 (A-11-1) 30cac 24 34.67 1236 12 7.4 40 20 297.5 88 206 - - - 596.8 89 11-19-97 (A-11-1) 18daa - 0.75 298 10.5 7.8 <5 <20 6 32 127 - - - 6.6 90 11-20-97 (A-12-1) 32bad 116 0.5 226 15.4 7.7 <5 <20 5 <10 5.53 - - - 213.4 90.5 11-19-97 (A-11-1) 2caa 191 3.58 334 11.3 7.5 <5 <20 9.5 <10 8.25 - - - 330.9 91 11-20-97 (B-12-1) 29dcc 103 0.4 230 14.7 7.8 <5 <20 6.5 11 7.97 - - - 184 91.5 11-19-97 (A-11-1) 3daa 154 <.02 280 9.4 7.7 41 1940 10.7 <10 18.1 - - - 247 92 11-19-97 (A-11-1) 17bdd 127 1.4 284 10.6 7.6 <5 <20 6.5 26 6.88 - - - 266.3 92.5 11-19-97 (A-11-1) 17aab 155 1.47 294 9.1 7.6 <5 <20 6.5 28 7.38 - - - 271.6 93 11-19-97 (A-11-1) 20cad 80 1.38 342 9.5 7.6 <5 <20 7.5 62 6.97 - - - 227.4 93.5 11-19-97 (A-11-1) 6daa 145 2.32 268 11.6 7.5 <5 <20 7.5 <10 12.8 - - - 178.3 94.5 11-19-97 (A-11-1) 7ddd 140 1.41 284 10.9 7.5 <5 <20 6.5 28 7.41 - - - 226.7 95.5 11-19-97 (A-11-1) 10caa 151 0.57 178 9.7 7.9 <5 <20 <3 <10 2.73 - - - 188.2 96 11-20-97 (A-12-1) 32dbc 98 <.02 248 9.8 7.8 24 2160 3.5 <10 5.52 - - - 241.1 96.5A 11-19-97 (A-11-1) 8ddc 138 1.58 294 10.8 7.5 <5 <20 7.5 23 7.21 - - - 287.7 " 11-19-97 (A-11-1) 8ddc 138 2.12 318 10.4 7.4 <5 <20 7.7 25 8.21 - - - 240.2 97.5 11-19-97 (A-11-1) 17dac 139 1.88 300 10.1 7.6 <5 <20 8.5 28 7.27 <2 <10 <.5 284.2 98 11-20-97 (A-12-1) 33bca 145 0.09 212 17.6 7.6 <5 22.4 5.5 <10 4.36 - - - 211.4 98.5 11-19-97 (A-11-1) 19aaa 138 0.7 270 11.9 7.6 <5 <20 7 43 5.36 - - - 235.1 99 11-19-97 (A-11-1) 9adb 191 3.14 286 10.2 7.5 <5 <20 6.5 12 8.45 - - - 260.1 99.5 11-19-97 (A-11-1) 28cab 164 2.14 346 11.2 7.5 <5 <20 9.3 61 6.92 - - - 311.2 100.5 11-18-97 (A-11-1) 33daa 232 0.51 302 - - <5 <20 6.2 62 5.56 - - - 240.3 101 11-19-97 (A-11-1) 32baa 140 0.26 328 10.9 7.5 <5 <20 5.5 94 5.66 <2 <10 <.5 253.4 102 11-19-97 (A-11-1) 9ddb 205 0.06 246 10.6 7.8 <5 842 8 <10 6.02 - - - 242.1 105 11-19-97 (A-11-1) 15bdc 143 9.71 452 11.1 7.3 <5 <20 29.5 28 16.5 - - - 258.1 106.5 11-19-97 (A-11-1) 18add 151 0.58 270 11.1 7.6 <5 34.8 6 30 5.59 - - - 245.1 107.5 11-19-97 (A-11-1) 9ccb 156 1.54 294 12.9 7.5 <5 <20 8.5 19 6.77 - - - 283.2 108 11-19-97 (A-11-1) 3dcb 127 0.83 356 10.5 7.3 <5 204 14 15 8.8 - - - 321.5 108.5 11-19-97 (A-11-1) 17bdd 131 1.16 284 10.6 7.6 <5 <20 5.5 26 6.63 - - - 190 109.5 11-19-97 (A-11-1) 29acc 131 1.25 324 9.9 7.7 <5 <20 100 64 6.78 - - - 259.5 410 12-16-97 (A-11-1) 16aaa - 3.91 368 8.7 7.4 <5 246 11 21 7.46 - - - 265.3 411 12-16-97 (A-11-1) 19dad - 4.03 546 12.7 7.4 <5 <20 56 83 41.2 - - - 260.4 110.5 11-18-97 (B-10-1) 10caa 210 0.89 236 8 7.8 <5 <20 6.5 <10 4.16 - - - 224.3 111 11-17-97 (B-10-1) 14cbc 200 0.76 386 11.4 7.3 <5 37.7 27.5 16 26.2 - - - 255 112 11-18-97 (B-10-1) 14bcc 87 1.6 506 - - <5 191 36.5 79 18.4 - - - 288.7 113 11-18-97 (B-10-1) 11bca 136 4.37 400 - - <5 <20 45 <10 20.5 - - - 351.9 114 11-17-97 (B-10-1) 14dcb 253 0.71 472 12.8 7.6 <5 23.9 152.5 15 62.2 - - - 290.7 115 11-17-97 (B-10-1) 14adb-1 80 15.04 476 10.3 7.3 <5 93.2 21 <10 25.9 - - - 201.2 " " 17.58 ------116 11-18-97 (B-10-1) 13bac 155 20.62 558 - - <5 <20 59 13 30 <2 424.8 " " 9.02 ------" " 21.33 ------117 11-17-97 (B-10-1) 12dda 250 11.91 476 8.4 7.5 7.3 28.9 27.5 12 23.6 - - - 321.2 " " 15.31 ------417 5-13-98 (B-10-1)13a 140 5.67 492 10.1 7.7 - - 39.5 33 35.2 - - - 302.2 419 5-13-98 (A-10-1)18a 160 9.13 828 9.4 7.4 - - 123 50 99.9 - - - 489 420 5-13-98 (B-10-1)7b 271 0.27 482 11.3 7.7 - - 57.5 15 43 - - - 317.5 421 5-13-98 (B-10-1)12d 178 1.99 250 12.3 7.7 - - 9 <10 8.3 - - - 235.3 118.5 11-18-97 (A-9-1) 11dcc 204 0.1 294 9.2 8 <5 145 23 <10 15.6 - - - 251.6 119 11-18-97 (A-10-1) 16cba 180 <.02 390 11.5 8 <5 241 23 <10 135 - - - 6.6 119.5 11-18-97 (A-10-1) 34ccb 200 3.75 444 10.4 7.4 <5 <20 24.5 10 23.6 - - - 338.2 120 11-18-97 (A-10-1) 9cba 300 <.02 384 9.6 7.4 6.1 1680 13.5 <10 17.7 - - - 253.3 120.5 11-18-97 (A-10-1) 10cdb 354 1.49 354 13.6 7.6 <5 <20 24 11 27.5 - - - 174.2 121 11-18-97 (A-10-1) 28caa 108 3.68 334 11.9 7.6 <5 <20 13 18 10.2 - - - 234.6 123 11-18-97 (A-10-1) 21caa 85 <.02 368 - - <5 2860 15 36 15.5 <2 - - 239.4 Total Well Field Fe, Chlor- Alpha, Beta, 226 Hardness/ Sample Depth NO2+NO3 TDS T Arsenic Dissolved ide SO4 Na gross gross Radium CaCO3 Site # date USGS Cadastral (feet) (mg/L) (mg/L) ((C) pH (g/L) (µg/L) (mg/L) (mg/L) (mg/L) (pCi/L) (pCi/L) (pCi/L) (mg/L) 124 11-18-97 (A-10-1) 9cdd 215 <.02 326 - - <5 1170 20 <10 24.1 3.44 - - 257.1 125 11-18-97 (A-10-1) 21dbd 96 5.73 410 12.5 7.6 <5 <20 15 18 24.9 - - - 344.9 126 11-18-97 (A-10-1) 15cbb 80 4.33 382 10.5 7.5 <5 <20 23 16 22.2 - - - 322 127 11-18-97 (A-10-1) 10bcc 323 4.53 344 10.9 7.4 <5 <20 18.5 <10 22.1 - - - 206.7 128 11-18-97 (A-9-1) 10bbc 90 1.8 318 11.2 7.4 <5 <20 13 <10 10.8 - - - 210.7 129 11-18-97 (A-9-1) 3cab 170 1.57 386 12.1 7.5 6.1 <20 22 12 19.4 - - - 319 131 11-18-97 (A-10-1) 10cdd 334 2.93 392 <5 <20 19.3 27 20.8 - - - 289 132 11-18-97 (A-9-1) 11bcc 64 4.17 360 10 7.8 <5 <20 22.5 10 14.4 - - - 333 133 11-18-97 (A-9-1) 10adc 80 2.31 328 <5 <20 12 12 11.5 - - - 303.7 APPENDIX B. Generalized stratigraphy of Cache Valley, Cache County, Utah and surrounding areas; sources of information (superscript numbers in Geologic Units column) from: (1) Bjorklund and McGreevy (1971), (2) Oviatt (1986a, b), (3) Hintze (1988), (4) Evans and others (1996), (5) Biek and others (2001). (ft = feet, m = meters)

FgjhshfghSystem Geologic Units Dominant Lithologies and Thickness Depositional Environment Hydrostratigraphic and Remarks Characteristics Surficial deposits 1,2,3,4 Consist of clay, silt, sand, gravel, and boulders Valley fill- primarily poorly Principal aquifer of Cache sorted, poorly stratified, alluvial, Valley. Has low to high colluvial, and mass-wasting permeability and yields small to deposits overlain by, or large quantities of ground interfingered with, lacustrine water.

Quaternary deposits of horizontally bedded, valley fill: 0-1,340 ft; 0-408 m well-sorted sediments from Quaternary lake cycles. Salt Lake Formation 1,2,3,4 Consists primarily of tuff, tuffaceous and calcareous Deposition by alluvial, colluvial, Generally low to moderate siltstone, sandstone, conglomerate, marl, and volcanic, and mass-wasting permeability. The fanglomerate freshwater limestone; white to light shades of tan, events. Some of the formation facies has high permeability brown, yellow, green, and gray. was waterlain and in part locally. Yields water to a few reworked. wells and springs. thickness: 0-6,100 ft; 0-1,859 m

Wasatch Formation 1,2,3,4 Red to reddish-brown conglomerate. Poorly sorted Conglomerate deposited by Generally low permeability; Tertiary clasts accumulated from erosion of surrounding alluvial, colluvial, and mass- however, solution of carbonates bedrock units. Matrix typically poorly consolidated wasting events in response to within formation has increased sand and/or silt. adjacent bedrock uplift during the permeability locally. Yields Sevier orogeny. water to many small springs, thickness: 0-460 ft; 0-140 m especially at basal contact.

Bear River Range

Wells Formation 2,5 Fine- to medium-grained, gray to brown, calcareous, Marine deposition. Ground water dependent on quartz sandstone and interbedded gray limestone. abundance of fractures and dissolution cavities.

Permian? thickness: 600-900 ft; 183-275 m Pennsylvanian/

Monroe Canyon Limestone 2,5 Upper part is gray to gray-brown cherty limestone; Marine deposition. Ground water dependent on middle consists of yellow-brown, medium-bedded, Contains corals, crinoids, chert, abundance of fractures and poorly exposed siltstone; lower is a gray to brown- and oolitic beds. dissolution cavities. gray, thick-bedded, massive, cliff-forming limestone.

Mississippian thickness: 560-1,150 ft; 171-351 m SystemFigure 1. continued.Geologic Units Dominant Lithologies and Thickness Depositional Environment Hydrostratigraphic and Remarks Characteristics Little Flat Formation 2,5 Gray, brown, light-yellow, and orange quartz Marine deposition. The Ground water dependent on sandstone and siltstone; with minor limestone, formation may thin northward, or abundance of fractures and phosphatic limestone, dolomite, shale, and chert. thickness may vary due to dissolution cavities. bedding plane thrust faults. thickness: 1,010-1,206 ft; 308-368 m

Lodgepole Limestone 2,5 Medium- to dark-gray limestone consisting of micrite, Marine deposition. Common Ground water dependent on biomicrite, and biosparite with chert layers fossils include brachiopods, abundance of fractures and

Mississippian throughout. corals, gastropods, and bryozoa. dissolution cavities.

thickness: 600-700 ft; 183-213 m Leatham Formation 2,5 Thin-bedded, gray, black, and brown siltstone and Marine deposition. Unit is Unit too thin to contain a limestone. sporadically present throughout substantial amount of water. the range. thickness: 0-90 ft; 0-27 m Beirdneau Formation 2,5 Upper part is 30 to 60 ft (10 to 20 m) thick, gray, Marine and marginal marine Ground water dependent on resistant limestone. Remainder is thin- to medium- deposition. Cross-bedding, thin abundance of fractures and bedded, gray, tan, yellow, and brown arenaceous laminations, ripple marks, and dissolution cavities. dolomite which grades upward to a predominantly tan, mud cracks are common. yellow, and white sandstone. Unit thins northward.

thickness: 524-1,087 ft; 160-331 m

Hyrum Dolomite 2,5 The upper part is a cliff-forming, massive, medium- to Marine deposition. Ground water dependent on dark-gray dolomite. Lower is thin- to medium- abundance of fractures and bedded, yellow, gray, and tan dolomite and limestone. dissolution cavities. Devonian thickness: 220-1,011 ft; 67-308 m

Water Canyon Formation 2,5 Upper part is purple, gray, brown, yellow, and white Marine deposition. Ground water dependent on interbedded dolomite, siltstone, intraformational abundance of fractures and breccia, and calcareous sandstone. The lower part is a dissolution cavities. light-gray, white, and light-brown, thin-bedded argillaceous dolostone with local intraformational breccia.

thickness: 210-600 ft; 64-183 m Laketown Dolomite 2,5 Massive, cliff-forming, light-gray, fine- and medium- Marine deposition. Contains Ground water dependent on crystalline, medium- to thick-bedded dolomite. sparse corals, brachipods, abundance of fractures and cephalopods, and algal mats. dissolution cavities. Silurian thickness: 1,150-1610 ft; 351-496 m System Siluria

Cambrian Ordovicain n St. CharlesFormation Garden CityFormation Formation Swan Peak Dolomite Fish Haven Bloomington Formation N ounan Limestone Geologic Units 2,5 2,5 2,5 2,5 2,5 2,5 thickness: 1 formation. N consists ofcrystallineandfossiliferouslimestone. Lenses of black chert are common. Lower part dolomitic limestone. light-gray limestone and minor partisthin- to medium-bedded, medium- to Upper 0-122 m thickness: 0-400; quartzite andgraylimestone. bedded thin- minor, brown and shalewith green, gray, blue, gray quartzite. Lower part isinterbedded purple and quartzite.Middlepart is indurated, medium-grained partislight-brown to white andtan, well Upper 0-149 ft; m thickness: 0-490 topofformation. near nodules present bioturbated sandy layers. Chert rare dolomite, with to fine medium black,thick-bedded, Dark-gray to hcns:1 thickness: l unitconsists of lower primarily ofmedium- toth consists themiddlerusty-brown silty limestone; unit to intercalatedorange with dark blue-gray limestone Upper member isolive-drab m 244-366 800-1,200; thickness: and sandstone. dark-graylimestone, siltylimestone, bedded, light-to Thin-bedded tomassive m 235-326 ft; 770-1,070 thickness: quartzite andarkose. gray, pink, and tan formation is light- ofthe Creek Member atthe base dark-gray; cont light- to Dolomite andlimestone, thin- tomedium-bedded, imestone. umerous intraformationa Dominant LithologiesandThickness , , 160-1 400-1 , , 400 500 ft nebde shale and interbedded ; iscetlyr.Worm ains chert layers. 354-427 m 354-427 dolomite. Thin-to medium- ; 427-457 m l conglomerate bedsin ick-bedded limestone; the olgtbonshale and to light-brown Marine deposition. N evidence ofbioturbation. and mats, tabulate and rugose coral, rarealgal remnants of contains structural thinning. Formation formation is due to of the deposition. Local absence Marine deposition. Marine and marginal-marine deposition. Marine and marginal-marine Marine deposition. and cephalopods. fragments, disarticulatedtrilobites brachiopod ripple marks, burrows, middle part contains part contains burrows; Upper Depositional Environment earshore-marine deposition. and Remarks dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. possibleminor fractures and primarily onabundance of Ground waterdependent dissolution cavities. abundance of fractures and on waterdependent Ground Shale layers act asaquitards. limestones. in interbedded fractures andsolution cavities presence dependent on water permeability. Ground Low Hydrostratigraphic Characteristics System

Pennsylvanian/ Percambrian Cambrian Permian Oquirrh Formation Mutual Formation Langston Formation Ute Limestone Blacksmith Limestone Geertsen CanyonQuartzite Geologic Units 2,5 2,5 1,5 2,5 2,5 2,5 hcns:450660 1,371-2,012 m 4,500-6,600; thickness: orange, and the limestones are lightgray. or brown yellowish generally weatherto limestone. Sandstones sandstone, sandy limestone and Interbedded thickness: 200-810 ft; 61-247 m 61-247 ft; 200-810 thickness: with the lowerpart is shale part middle part is dolomite, Upper green, and tan. grey, mudstone; colors are unitconsistsofdolomite, limestone, shale,and This m ft; 122-244 400-800 thickness: dolomite exposed brown to tan Thin-bedded unit. throughout interbedded fissileshale Olive-drab dark-gray, siltylimestone. Medium- tothin-bedde m 101-213 ft; 330-700 thickness: dolomite. Interbedded siltylimestone, siltstone,and limestone. dark-gray Medium- tothin-bedded, light-gray to thickness: 1,128 ft; 343 m 343 ft; 1,128 thickness: topale-purple orpinkquartzite. pebbly, grayish-red Coarse- tomedium-grained, commonly gritty,locally thickness: 2,225-2,550 ft; 678-777 ft; m 2,225-2,550 thickness: unit. abundance towardthe base of the occurthroughout unitand increase in small pebbles pu paleredor with streaked whiteorflesh-pink quartzite,locally Pale-buff to Dominant LithologiesandThickness d, finely crystalline, light- to is predominantly shale,and Wellsville Mountains tbs fformation. at base of interbeded limestone. rple. Coarse grained; (550m). ft 1,800 above formation in Fusulinids determine thickness. formation, making in hard to colluvium typically covers the of deposition. Thin layer Marine fossils. Abundant Marine deposition. E deposition. Triolobite Marine limestone common. Oolitic Marine deposition. N N Abundant cross-bedding. Depositional Environment hmaniella earshore marine deposition. marine earshore earshore-marine deposition. and Remarks rsn nbslunits. present inbasal najcn OgdenValley. in adjacent apparently flowsata high rate wellinformation One fracture density. on of water dependent Presence water. ground amounts of supports large often High fracturedensity; dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on water dependent Ground Hydrostratigraphic Characteristics System

Devonian Mississippian Pennsylvanian Beirdneau Formation Deseret Limestone Humbug Formation Limestone Great Blue Limestone West Canyon Lodgepole Limestone Geologic Units 1,5 member Upper member Lower 1,5 1,5 1,5 1,5 1,5 thickness: 0-347 ft; 0-106 m 0-106 ft; 0-347 thickness: dolomitic sandstone. dolomiteor sandy minor and shale, yellowish-orange dolomite, interbedded Medium- tolight-gray hcns:80f;250 m 820 ft; thickness: or limestone. interbedded sandy limestone with dolomitic sandstone Brown, calcareous, 168 m 550 ft; thickness: Medium- todark-gray, cliff-forming limestone. 156 m 475 ft; thickness: shaleand limestone. interbedded olive-gray partis graylimestone. Lower partischerty Upper 145 m 400 ft; thickness: minor shale. sandylimestone, and chertylimestone, Medium-gray, hcns:90f;296 m 970 ft; thickness: forming. Chert common incliff-forming units. partsare cliff forming; themiddle isslope lower Medium- todark-gray 91ft;28m thickness: part. phosphatic shale andblack chert inlower Cherty limestone and minor sandstone, thin Dominant LithologiesandThickness ietn. h pe and upper The limestone. Marine deposition. corals, are common throughout. oolitic;fossils,particularly are deposition. Some beds Marine Marine deposition. I deposition. Contains Marine conodonts. and brachiopods, gastropods, preserved crinoids, corals, well- abundant including Fossils Marine depositon. Marine deposition. Range. Flat Formation inthe BearRiver Little ofthe part with theupper Mountains islikelycorrelative Wellsville Formation inthe Humbug deposition. The Marine Depositional Environment diognathodus. and Remarks dissolution cavities. abundance of fractures and on waterdependent Ground water. of substantial amount Unit istoo thintocontaina dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on water dependent Ground Hydrostratigraphic Characteristics System

Ordovician Silurian Devonian Garden CityFormation Fish Haven Dolomite Fish Haven Dolomite Laketown Formation Water Canyon Hyrum Formation wnPa Formation Swan Peak Geologic Units 1,5 1,5 Lake Member Tony Grove Upper Card Member Member Grassy Flat 1,5 1,5 1,5 1,5 thickness: 1,334-1,390 ft; 407-424 ft; m 1,334-1,390 thickness: beds. total volume of certain ofthe occupy more than 50 percent beds and may theupper limestone conglomerate; chert iscommon in Limestone, siltylimestone, andintraformational hcns:51ft;171m thickness: 561 ofsilica. blobs and strings unitcontains chert nodulesand irregular feet oflower Upper 60 crystallinedolomite. Medium-gray, finely 168 m 550 ft; thickness: Light- tomedium-gray, coarselycrystallinedolomite. 131 m 428 ft; thickness: dolomite. Light-gray weathering, very 261 m 857 ft; thickness: interbedded dolomite. fine- orange-weathering, fine white Light-gray to m 149 ft; 490 thickness: Valley. southern part ofCache in the out pinch which Includes several localquartzite beds, me Dark- tomedium-gray hcns: 030f;15-91 m 50-300 ft; thickness: gray shale in lowerpart. partis white topurp Upper 60m 197ft; thickness: formation. dolomite atthebase of dolomite. Sandy, bioturbated Medium- todark-gray Dominant LithologiesandThickness -grained dolomite, grayish- grained sandstone, and dium-crystalline dolomite. eqatie akolive- Dark le quartzite. fine-grained laminated rpoie,adgastropods. and graptolites, brachiopods, cephalopods, shale include trilobites, deposition. Fossils in Marine Marine deposition. contain small gastropods. oflimestone few thinbeds andchertnodules.A fragments sandstones containfish-bone deposition. Some ofthe Marine Marine deposition. rpoie,andostracods. graptolites, brachiopods, cephalopods, shale include trilobites, deposition. Fossils in Marine formation. abundant in corals and small rugose corals are deposition. Colonial Marine brachiopods. andsilicified rugose corals, deposition. Contains Marine brachiopods. rugose coralsandsilicified deposition. Contains Marine N Depositional Environment onfossiliferous. and Remarks abundance of fractures. on waterdependent Ground water. of substantial amount Unit istoo thintocontaina dissolution cavities. abundance of fractures and on waterdependant Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on water dependent Ground Hydrostratigraphic Characteristics System Geologic Units Dominant Lithologies and Thickness Depositional Environment Hydrostratigraphic and Remarks Characteristics Ord. St. Charles Dolomite Thin- to thick-bedded, finely to medium-crystalline, Marine deposition. Moderately fractured limestone. Limestone 1,5 member light- to medium-gray, cliff-forming dolomite. Pink Source of Bluerock Springs in chert common in member. adjacent Box Elder County.

thickness: 990 ft; 302 m

Worm Creek Thin-bedded, fine- to medium-grained, medium- to Nearshore marine deposition. Less fractured than upper Quartzite dark-gray, calcareous quartzitic sandstone. Grains are member. Formation is too thin Member well-rounded and well-sorted. to hold a substantial water supply. thickness: 70-178 ft; 21-54 m

Ground waterN ounandependant onUpper abundance of fracturesInterbedded and dolomite, dissolution sandy dolomite,cavities. dolomitic Marine deposition. Limestone is Ground water dependent on Dolomite 1,5 sandstone, and thin limestone. fossiliferous. abundance of fractures and dissolution cavities. thickness: 545 ft; 166 m Lower Thin- to thick-bedded, finely crystalline, medium- Marine deposition. Ground water dependent on gray, cliff-forming dolomite. abundance of fractures and dissolution cavities. thickness: 729 ft; 222 m

Cambrian Bloomington Calls Fort Shale Olive-drab to light-brown shale and dark blue-gray Marine deposition. Low permeability. Water Formation 1,5 Member limestone with intercalated orange to rusty-brown presence dependent on fractures silty limestone; intraformational conglomerate and solution cavities in common throughout unit. interbedded limestones.

thickness: 300 ft; 91 m

Middle Cliff-forming, thin- to very thick-bedded medium- Marine deposition. Ground water dependent on limestone gray, cliff-forming limestone, oolitic limestone, and abundance of fractures and member local intraformational limestone conglomerate. dissolution cavities.

thickness: 650 ft; 198 m

Hodges Shale Slope- and ledge-forming, thin-bedded, medium-gray Marine deposition. Ground water dependent on Member limestone, oolitic limestone, and intraformational abundance of fractures and conglomerate with lesser interbedded light olive-gray dissolution cavities. shale.

thickness: 330 ft; 101 m System

Precambrian ? Cambrian Langston Formation Ute Limestone Blacksmith Limestone Brigham Group 1,5 Geologic Units Formation Hole Browns Quartzite Canyon Geertsen Inkom Formation Mutual Formation 1,5 1,5 member Lower member Quartzite 1,5 hcns:40f;122 m 400 ft; thickness: to tan. Dolomite, limestone, shal thickness: 3,500 ft; 1067 m 1067 ft; 3,500 thickness: downsection. clasts increase feldspar m) isstronglyarkosic,and (90-120 ft 365 275to section. Basal down decreases inabundance streaks andlenses ofcobble conglomerate that quartzitewithirregular whiteandtan Pale-buff to 198 m 650 ft; thickness: dolomite exposed brown to tan Thin-bedded unit. throughout interbedded shale fissile Olive-drab dark-gray siltylimestone. Medium- tothin-bedde 244 m 800 ft; thickness: dolomite. Interbedded siltylimestone, siltstone,and limestone. dark-gray Medium- tothin-bedded, light-gray to hcns:34f;120 m 394 ft; thickness: tuff. siltstone; lower part islight gray-weathering olive-drab laminated by dark-green to underlain fine-grained Upperis very part 670-790 ft; m 2,200-2,600 thickness: topale-purple orpinkquartzite. pebbly, grayish-red Coarse- tomedium-grained, commonly gritty,locally m 76-107 ft; 250-350 thickness: breccias. scoriaceous to to black, red Locallyunderlain by terracotta-colored quartzite. well-sorted, well-round, Medium- tofine-grained, Dominant LithologiesandThickness d, finely crystalline, light- to aydlia volcanic amygdoloidal tbs fformation. at base of n usoe gray, green e andmudstone; akgensandstone , dark-green Marine deposition. Marine deposition. Marine deposition. N N N deposition. Marine and marginal marine Abundant cross-bedding. quartzite. bedding in Small tolarge-scalecross- Depositional Environment earshore marine deposition. marine earshore deposition. marine earshore deposition. marine earshore and Remarks fracture density. on of water dependent Presence fracture density. on of water dependent Presence abundance of fractures. on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground Low permeability. Hydrostratigraphic Characteristics System

Ordovician Ordovician/ Pennsylvanian/ Precambrian Silurian Permian wnPa Formation Swan Peak undifferentiated Formation Swan Peak HavenDolomite, Fish Laketown Dolomite, Oquirrh Formation FormationKelley Canyon Papoose Creek Formation undifferentiated Dolomite Fish Haven Laketown Dolomite Brigham Group Geologic Units Caddy Canyon Quartzite Canyon Caddy 4,5 4,5 4,5 4,5 1,5 1,5 hcns:574ft thickness: limestone. shal interbedded olive-gray f withabundant orthoquartzite forming, thin-to medi ledge- feet m) and 100 (30 ofslope- consists Lower whitetogr thick-bedded, very forms prominent cliffsand ledges of part Upper hcns:450660 1,371-2,012 m 4,500-6,600; thickness: light-gray. an yellowish-brown or orange, generally weatherto limestone. Sandstones sandstone, sandy limestone, and Interbedded m 215 700ft; thickness: dark-grayan has alternating gray, andsilver; commonly gray, greenish to tan, dark dark-graytobl Thin-bedded, m 228-457 ft; 750-1,500 thickness: an wavy, Thin, sandstone. quartzitic to greenish-gray,fine-grained light-gray olive-drabsiltstone withinterbedded Dark-gray to m 305 ft; 1,000 thickness: purple. green, or generally tan,gray, rocks are quartzite. Part of unitmay belight-grayto white,but Medium-grained, medium- to thickness: 2,100 ft; 640 m 640 ft; 2,100 thickness: nodules andlenses. chert crystalline dolomite with coarsely Medium- tovery thick-bedded, medium- to brecciated, fault-bounded blockShort Divide. near ina found are formations Thesethree Mountains. Wellsville Lithologies similar tothosein the Dominant LithologiesandThickness ; 175 m um-bedded, moderate-brown lclbakandlight-brown localblack yt ikorthoquartzite. pink ay to Clarkston Mountain icniuu bedding. d discontinuous ,and minor thin-bedded e, greenish-gray interbeds. d ack argillite,weathering tikbde,vitreous thick-bedded, ucoidal markings; lesser d thelimestones are aiedeposition. Marine Marine deposition. Marine deposition. Marine deposition. Marine deposition. Marine deposition. (550m). in formation areabove 1,800 ft Fusulinids determine thickness. formation, making ithard to colluvium typicallycovers the of deposition. Thin layer Marine Depositional Environment and Remarks dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground dissolution cavities. abundance of fractures and on waterdependent Ground fracture density. on of water dependent Presence fracture density. on of water dependent Presence fracture density. on of water dependent Presence abundance of fractures. on water dependent Ground Hydrostratigraphic Characteristics System Geologic Units Dominant Lithologies and Thickness Depositional Environment Hydrostratigraphic and Remarks Characteristics Garden City Formation 4,5 Limestone, silty limestone, and intraformational Marine deposition. Ground water dependent on limestone conglomerate; chert is common in the upper abundance of fractures and beds and may occupy more than 50 percent of the dissolution cavities. total volume of certain beds. Ordovician thickness: 1,764 ft; 538 m

St. Charles Upper Thick- to very thick-bedded, medium- to dark-gray, Marine deposition. Ground water dependent on Limestone 4,5 medium- to coarsely crystalline dolomite, with local abundance of fractures and light-brown chert nodules. dissolution cavities.

thickness: 700 ft; 213 m

Middle Thin- to medium-bedded, medium-gray limestone Marine deposition. Ground water dependent on with thin interbeds of intraformational limestone abundance of fractures and conglomerate and fossil hash throughout. dissolution cavities.

thickness: 250 ft; 76 m

Lower Interbedded, thin-bedded, silty and sandy carbonate Marine deposition. Ground water dependent on between two beds of medium- to very thick-bedded, abundance of fractures and gray to brown to red feldspathic sandstone. dissolution cavities.

thickness: 70 ft; 21 m

Nounan Upper Thin- to medium-bedded, light- to dark-gray, locally Marine deposition. Ground water dependent on 4,5 oolitic, variably sandy and silty dolomite and abundance of fractures and

Cambrian Dolomite limestone, and interbedded, locally iron-stained and dissolution cavities. micaceous calcareous siltstone and fine-grained sandstone.

thickness: 500 ft; 152 m

Lower Cliff-forming, thick- to very thick-bedded, medium- Marine deposition. Ground water dependent on to coarsely crystalline, light- to medium-gray abundance of fractures and dolomite. dissolution cavities.

thickness: 800-1200 ft; 244-366 m

Bloomington Calls Fort Shale Brown-weathering, laminated to very thin-bedded Marine deposition. Low permeability. Water Formation 4,5 Member shale and micaceous siltstone with some interbedded presence dependent on fractures gray limestone and intraformational conglomerate. and solution cavities in interbedded limestones. thickness: 429 ft; 131 m System Geologic Units Dominant Lithologies and Thickness Depositional Environment Hydrostratigraphic and Remarks Characteristics Bloomington Middle Thin- to very thick-bedded medium-gray, cliff- Marine deposition. Ground water dependent on Formation4,5 limestone forming limestone, oolitic limestone, and local abundance of fractures and member intraformational limestone conglomerate. dissolution cavities.

thickness: 444 ft; 135 m

Hodges Shale Slope- and ledge-forming, thin-bedded, medium-gray Marine deposition. Ground water dependent on

Cambrian Member limestone, oolitic limestone, and intraformational abundance of fractures and conglomerate, and lesser interbedded light olive-gray dissolution cavities. shale.

thickness: 439 ft; 134 m